Hillary Clinton’s easiest path to an Electoral College majority does not include Ohio, Florida, or North Carolina.

Yet those three states all rank at the very top of the list of locales where she has invested the most time and advertising spending, especially in the campaign’s critical closing weeks. By contrast, the campaign has devoted very little advertising or time from Clinton and her top surrogates in several of the states that are part of her core strategy for reaching 270 Electoral College votes—among them Michigan, Wisconsin, Colorado, Virginia, and New Mexico.

The Clinton team’s decision to focus so much more attention on states that it wants to win—as opposed to those it believes it needs to win—represents one of the central, if often unremarked upon, choices of the 2016 election. It has allowed her to play offense for most of the general election, while forcing rival Donald Trump to spend most of his energy defending states more indispensable to his strategy than to hers.

But it’s also meant Clinton has devoted little attention, beyond field organizing, to fortifying states where Trump is now making a late push amid the tailwind of tightening national polls. With Trump consolidating traditional Republican voters, Clinton faces the risk that she has overestimated her hold on the places most central to her strategy.

Put another way, as Clinton has focused her time and money primarily on swing and Republican-leaning states, the question looming over her campaign is whether she has left herself open to a flanking maneuver from Trump in any of the seemingly safe Democratic states that he is now targeting—key among them Colorado, Michigan, and Wisconsin. “For a Republican nominee to breach the ‘blue wall’ of Wisconsin and Michigan, they need to invest in those states and hope for a national tide to come in,” said Brent McGoldrick, the co-founder of the Republican voter-targeting firm Deep Root Analytics. “It’s possible she left herself open to that breach.”

Clinton and her allies are responding with a new wave of advertising and more surrogate appearances in those blue-leaning states, and most dramatically, a visit by Clinton herself to Detroit on Friday. But overall they see Trump’s late push into these Democratic-leaning places as a sign of weakness, not strength—an admission that at this late date he needs new options for reaching an Electoral College majority because he cannot feel secure of capturing enough of the states both sides consider true battlegrounds. Democrats took heart in a wave of polls released Wednesday that showed her still leading in Wisconsin and Pennsylvania, though with diminished margins in the latter.

Democratic strategists have almost universally cheered Clinton’s aggressive Electoral College strategy, believing it provides her multiple pathways to reach a majority if Trump makes an unanticipated breakthrough in her core states, particularly one of the 18 “blue wall” states that have voted Democratic in every presidential election since at least 1992. “I’m glad she is on the offensive expanding the map, rather than raising the barriers to Trump breaching the blue wall,” said longtime Democratic pollster Stanley B. Greenberg. “I also think the strategy flowed from the successful debates where they had the momentum. The Russians [through WikiLeaks] and FBI choose to throw some roadblocks in the way. … Still, offense was a better choice than defense.”

Mitch Stewart, the field director for President Obama’s 2012 campaign, takes a similar view. “What that Clinton strategy allows is to withstand the unprecedented nature of what the FBI announcement was,” he says, referring to FBI Director James Comey’s letter to Congress on Friday. “They have built up multiple firewalls to defend themselves.”

Republican pollster Glen Bolger says that against a different Republican candidate Clinton could not have afforded to devote so little effort to defending places like Michigan, Wisconsin, Virginia, and Colorado. But he’s dubious Trump can succeed in his late incursions there because he did not make a more consistent effort in those states earlier in the campaign—much less build strong in-state organizations. “It might be true [that Clinton has exposed herself to risk] if the Trump strategy wasn’t wake up, pick up a dart, throw it at a map, and say ‘That’s where we are going today,’” Bolger said.

Even so, McGoldrick says that in October Trump outspent Clinton and her allies on television by about seven-to-one in Wisconsin and two-to-one in Colorado. “This strategy does leave her exposed, particularly in Wisconsin,” he says.

Almost all analysts agree that Clinton has more plausible options for reaching an Electoral College majority than Trump does. And among analysts from both parties, there’s broad agreement about the states that offer her the most straightforward path to victory. That path starts with the 18 states that form the blue wall, a term I coined in 2009. These states have backed the Democratic nominee in at least the past six presidential elections; together with the District of Columbia, they offer 242 Electoral College votes.

The blue-wall states include the eleven states from Maryland to Maine, except for New Hampshire; Michigan, Minnesota, Wisconsin, and Illinois in the upper Midwest; the three West Coast states of California, Oregon, and Washington; and Hawaii. Of those, the states usually considered the most competitive for Republicans are Michigan, Wisconsin, and Pennsylvania. That may be especially true for Trump this year, given his strength among working-class white voters, who are prevalent in all three states, and his weakness among the minority and white-collar whites more numerous in other blue-wall states.

Clinton’s electoral map thus starts with defending Pennsylvania, Michigan, and Wisconsin, the three loosest bricks in the blue wall. (Of the remaining blue-wall states, perhaps only Maine might be plausibly at risk to Trump.) After that, both sides agree her easiest pathway to a majority runs through three heavily diverse Sunbelt states: There’s New Mexico, which has voted Democratic in five of the past six elections; and then Colorado and Virginia, which have moved from Republican-leaning in the 1990s, to closely contested in the first decade of this century, to Democratic-leaning at the presidential level since 2008. The last piece in the most direct path for Clinton is New Hampshire, a state where she struggled during the primaries, but has led in almost all polls during the general election.

If Clinton holds the 15 blue-wall states that neither side sees as seriously contested, and adds the seven core states of Pennsylvania, Michigan, Wisconsin, New Mexico, Colorado, Virginia, and New Hampshire, she amasses 273 Electoral College votes. That means she wins regardless of what happens in any other battleground, including Florida, North Carolina, and Ohio. She still holds a narrow majority of 272 Electoral College votes even if Trump wins the rural second district in Maine, one of the two states that awards Electoral College votes by congressional district.

Yet of those seven core states, the Clinton campaign and Priorities USA—the principal super PAC supporting her—has treated only Pennsylvania and, to a somewhat lesser extent, New Hampshire as true battlegrounds. The tally of campaign advertising spending maintained by Ad Age and Kantar Media’s Campaign Media Analysis Group shows that through late October, Clinton had spent almost $38 million in Pennsylvania and over $28 million in New Hampshire, but only about $23 million combined in Michigan, Wisconsin, Colorado, and Virginia. New Mexico had attracted almost no spending from either side through that point.

Clinton aides underscore that they have maintained robust organizing efforts in the other core states beyond Pennsylvania and New Hampshire. But they have trained the biggest guns in their arsenal—their advertising dollars and the time of Clinton and top surrogates, such as President Obama and First Lady Michelle Obama—elsewhere.

While Clinton has not visited Wisconsin since April, and appeared just twice in Michigan from June through October, she has virtually taken up residence in Florida, North Carolina, and—after a long absence in September—Ohio. Since June 1, Clinton has appeared 12 times in Ohio, 11 times in Florida, and eight times in North Carolina, according to the campaign tracker maintained by National Journal’s Hotline. Among the core states, only Pennsylvania, with nine appearances, has received anything close to that much attention. Over that same period since June, she’s visited New Hampshire and Colorado three times each, Michigan twice, and Wisconsin not at all. Among states that are more of a reach for Clinton, she’s also visited Nevada four times and Iowa three times. After long consideration, the campaign is making a late push in Arizona, which Democrats have carried only once since 1948; Clinton is visiting the Phoenix area on Wednesday.

Except for Arizona, these states have received enormous advertising spending as well: The Ad Age/Campaign Media Analysis Group tally puts the total at over $26 million in Nevada, about $31 million in Iowa, nearly $34 million in North Carolina, over $52 million in Ohio, and a breathtaking $93.8 million in Florida. Even Georgia has drawn some late Democratic money, if not time from the candidate or her top allies.

Analysts on both sides see strong arguments for Clinton lavishing so much attention on this group of states, even though she does not need any of them to win. Except for Ohio and Iowa, the rest of her “reach states” are all Sunbelt battlegrounds with growing populations of minority voters who reflect the increasingly diverse electorate. Pushing so hard in these Sunbelt states, Greenberg says, “aligns her with the trends of the country and allows for a bigger win.”

One Clinton adviser says her travel schedule has reflected not only the campaign’s priority on each state, but the needs of its organizing efforts; her last visit to Michigan, for instance, came the day before its voter-registration deadline. Her frequent trips to Florida and North Carolina have been tied to her early-voting efforts in both places. “Her travel is not just about press attention. … The trips are also about organizing,” the adviser said.

The reach states also offer Clinton her clearest chance at a knockout blow, because while she does not need to win them, Trump does. In particular, it’s very difficult, if not impossible, to imagine him reaching 270 Electoral College votes if he does not carry both Florida and Ohio, and likely even North Carolina. At the least, she’s forced Trump to also focus on states that he needs more than she does: The Hotline tracker shows that since June 1 he has made a combined 39 appearances in Florida, Ohio, and North Carolina, compared with a combined 15 in Michigan, Wisconsin, and Colorado—all states he’s now targeting. “He’s had to fight the last five months playing defense rather than offense,” says Stewart, a founding partner at the Democratic consulting firm 270 Strategies.

Trump’s limited resources also made this choice easier for Clinton. Despite her limited advertising buys in most of her core states, the Ad Age/CMAG tracker shows her outspending Trump in all of them except for Wisconsin.

Alex Lundry, the other co-founder of Deep Root Analytics, adds one other consideration: Many of the reach states that Clinton is targeting also have contested Senate races, including Nevada, North Carolina, and Florida. “This looks to me like ‘rational over-confidence,’” Lundry said in an email. “They likely continued to focus on those ‘reach states’ both to block his path, with the added benefit they are states with competitive Senate races. So by focusing there, she could effectively block him and help Democrats win the Senate.”

Yet all of those calculations will look that much wiser if Clinton holds her core states. If Trump pries any of them away while she has focused so much attention on these reach states, her team could face substantial second-guessing. In some ways, their situation is like a general who has sent out a large expeditionary force and left modest forces to defend their homeland. That works so long as the other side doesn’t land an expeditionary army of its own.

Can Trump execute such a maneuver?

Polls through the fall have consistently shown Clinton leading in all of the seven plausibly competitive states on her core list. In the averages posted Wednesday morning on HuffPost Pollster, Clinton leads by eight percentage points in Virginia, seven in Pennsylvania, six in Wisconsin and Michigan, and five in New Hampshire and Colorado. There’s been much less polling in New Mexico, where the average gives her a nine-point lead.

Despite the overall tightening in the race, most Democrats and many Republicans remain dubious that Trump can crack any of the states in Clinton’s inner circle of 273 Electoral College votes. On Wednesday, longtime GOP strategist Mike Murphy, a frequent Trump critic, tweeted: “Having done 4+ successful statewide GOP races in MI, I’ll put it this way: if Trump carries MI, I’ll die my hair orange.” Clinton maintained a six-point advantage in the highly anticipated Marquette Law School Poll of Wisconsin released Wednesday afternoon.

Still, some other individual recent surveys, most of them Internet-based, have shown Trump at least somewhat closer in Wisconsin, Michigan, and Colorado; more consistently, the latest polls have shown him narrowing a double-digit deficit to about five or six percentage points in Virginia and New Hampshire. Trump narrowed his deficit to only four points in two Pennsylvania surveys released Wednesday, but Clinton is campaigning much more aggressively there than in these other five states. (She’s appearing with Katy Perry at a Philadelphia rally on Saturday.)

The Clinton campaign has responded to Trump’s push with a new ad buy described as six figures each in Colorado, Virginia, Michigan, and New Mexico, as well as a separate purchase in Wisconsin. Meanwhile, Priorities USA, the pro-Clinton super-PAC, has returned to the air in Wisconsin and Colorado. One strategist familiar with the PAC explained its thinking this way: “We have the money. Why not buy some insurance? We advertised early in Wisconsin and Colorado. We always had returning to the air there as an option. No big shock we are doing so, given the high percentage of high-school-educated white voters [there].”

Still in the last days of a campaign that has proven more competitive than most Democrats expected, Clinton and her allies are still directing most of their dollars to the reach states beyond her inner core. According to figures reported by National Journal analyst Charlie Cook, Florida, Ohio, North Carolina, and Nevada all rank in the top five of states that the Clinton camp has reserved the most television advertising in the final week. Among the core states, only Pennsylvania makes that list. Even after all the tumult of the past week, Democrats are still betting that the surest path to victory is to fight mostly on terrain that Clinton can win without.

Assistant editor Leah Askarinam contributed.