Hundreds of thousands of ads have run millions of times during the 2014 campaign. Amid that flood of endorsements and attacks, slogans and statistics, it was easy to overlook the web ad put out on Tuesday by Kentucky Senate candidate Alison Lundergan Grimes. The web-only spot features former Secretary of State Hillary Clinton at a rally in Louisville, delivering a impassioned argument for the Democratic challenger.

It's a very standard spot that stands out for one very significant reason: It's the only ad that Clinton has cut for a candidate this election cycle. 

Though she's traveled the country for Democrats, headlining rallies from Colorado to North Carolina, Clinton has not lent any of her star power to any televised campaign ads. It's a strange discrepancy: While Clinton is one of—if not the most—requested surrogates for Democratic congressional campaigns, many seem far less seem eager to put her in their television ads.

Even the spot for Grimes, a long-time family friend of the Clintons, was online-only—a far less expensive proposition for a campaign than actually buying time to place an ad on television. And it used footage captured two weeks ago at a rally Clinton held for Grimes in Louisville, rather than any new video. 

http://www.youtube.com/watch?v=mt-7D2Esoe0&feature=youtu.be

Old footage of Clinton was also heavily featured in a House Majority PAC spot, where the Democratic super-PAC slammed Virginia Republican Barbara Comstock for her work as a congressional staffer in the 1990s focused on investigating the Clinton administration. 

But mostly, Clinton has kept to fundraising appeals and energizing voters. She's hosted a series of high-dollar fundraisers, including one for female Senate candidates at her home in Washington. Democrats need "all hands on deck," she wrote in an e-mail sent last month by the Democratic Congressional Campaign Committee. 

Hillary Clinton's spokespeople refused to comment on her ad appearances, or lack of them. But people close to the former first couple say they've been turning down requests from candidates to star in ads, fearing that if they cut a spot for one, they'd have to do them for everyone who asked. Those people say former President Bill Clinton is annoyed by several unauthorized usages of his image in ads.

While Hillary Clinton stays off TV, her husband has appeared in at least five ads for candidates. 

"Sean Maloney’s got a better jobs plan. He’s got a better budget plan. He’s got a better education plan. He’s got a better plan for the future," says the former president in a spot for the New York lawmaker, a former Clinton administration staffer. 

In Maryland, he urges voters to back gubernatorial candidate Anthony Brown in a spot featuring a shot of Clinton walking besides the Democrat. 

And he also lent his support for Grimes, whose father was a former state Democratic party chairman. (As a teenager, Grimes famously handed Clinton a bouquet of flowers during his inauguration celebration.)

"I chose Alison," Clinton says in a spot for the Kentucky Democrat.

"I'm honored to approve this message," says Grimes. 

https://www.youtube.com/watch?v=jWuMp6TRcYM

But it's an open question how effective a state-wide Hillary Clinton ad would be with independent voters in purple states. Her approval rating trails her husband's and has fallen since she left the State Department early last year. 

In the recent Bloomberg News/Des Moines Register poll almost half—49 percent—of likely Iowa voters in the upcoming midterm elections say they have an unfavorable view of Clinton, while 47 percent rate her favorably. Fifty-seven percent of likely voters have a positive opinion of her husband and 39 percent view him negatively. 

So, while Democrats at campaign rallies may love Clinton, she remains a nationally divisive figure, one that's perhaps too divisive for state-wide television. She's in high-demand as a base motivator but faces a steeper climb with the general public—an issue that will certainly come back up in any Democratic presidential bid. Especially her own.