The Republicans still hold an edge in what has become a very stable fight for the Senate, according to the last round of data from the New York Times/CBS News/YouGov survey of nearly 100,000 respondents.
The Republicans lead by four percentage points or more in enough states to finish with 50 seats, just one short of the 51 they need to overcome Vice President Joe Biden’s tiebreaking vote in the Senate. The Republicans could go over the top by holding Georgia, where their candidate maintains a slight lead, according to YouGov, or by winning one of two very close races, Colorado and Iowa. Other recent polls have showed the Republicans with a small lead in Colorado and Iowa and a virtual dead heat in Georgia and Kansas.
Democrats hold slight leads of their own in North Carolina and New Hampshire. Republicans hold modest leads of at least four percentage points in Kansas, Alaska, Louisiana, Arkansas and Kentucky, according to YouGov.
Every respondent in this wave of data participated in one of the previous three waves of surveys, and it is clear that voter preferences remain extremely stable. Ninety percent of respondents in the battleground states supported the same candidate as they did when they were last contacted. For the most part, respondents who changed their answers switched in or out of the undecided column, and these few shifts tended to cancel out: Respondents from the last wave shifted by a net of more than 1.8 percentage points in just one battleground state.
YouGov Estimates of the Vote in the Most Competitive Senate Races
* Poll refers to a runoff election between Senator Mary Landrieu and Bill Cassidy.
Other and undecided responses are not shown.
Source: YouGov (CBS/New York Times 2014 Election Panel, conducted Oct. 16 - 23, 2014)
That state was Kansas, where the Republican senator Pat Roberts now leads by four percentage points. It was a tie two weeks ago.
The good news for the independent candidate in Kansas, Greg Orman, is that Mr. Roberts has just 42 percent support. There are far more undecided voters in Kansas than elsewhere, which makes Mr. Roberts’s lead more vulnerable. The great news for Republicans is that it seems fairly clear how undecided voters are breaking: a net 5.5 percent of respondents were previously undecided and switched to Mr. Roberts. This is the first movement of this scale in any competitive state in the YouGov data so far this year.
The newfound G.O.P. advantage in Kansas changes the Senate math to the advantage of Republicans. To overcome a loss in Kansas, Democrats would need to win Iowa and Colorado, and then pull off an upset in one of the states where they trail, like Georgia, Alaska, Louisiana, Arkansas or Kentucky.
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Democrats cannot count on winning both Iowa and Colorado. The Democratic senator Mark Udall’s lead continued to shrink in the new survey, down to a nominal edge of one percentage point, well within the survey’s modeled margin of error. There was no change in the overall result in Iowa, where the race remains a dead heat — although past panelists there moved by a net 1.3 points toward Bruce Braley, the Democrat.
In the red states where Democrats trail, the YouGov data suggests that a Democratic upset is more plausible in Georgia or Alaska than Louisiana, Arkansas and Kentucky.
In Georgia, the Democrat Michelle Nunn trails by three points among likely voters, the smallest margin of any of the states where Republicans lead. But Ms. Nunn holds a nominal lead among registered voters, and she is the only Democrat who trails in the likely-voter screen. The data, however, does not show Ms. Nunn making substantial gains among past respondents over the last few weeks, calling into question whether the Republican David Perdue’s comments about outsourcing have changed the race as much as other polls have suggested.
In Alaska, there are several reasons for uncertainty, including the difficulty of polling in the state and the quality of the sample. Polling has long been unreliable in Alaska, and the YouGov data includes 561 respondents, fewer than in other states. As a result, the modeled margin of error is 8.6 percentage points.
The Alaska numbers nonetheless include one data point that should be encouraging to Democrats: A staggering 43 percent of registered voters say they’ve been contacted by the Begich campaign, more than in any other campaign in any battleground state. This appears to reflect huge Democratic investment in field operations in a state with a population smaller than some congressional districts: Just 7,500 additional votes would allow Democrats to close a three-point deficit.
Barring other surprises, if Democrats pull an upset in Kansas, Georgia or Alaska, they will need to win Iowa and Colorado to preserve their majority. It is a long and unlikely path to victory, but it is not one that can be ruled out based on this data alone. It cannot be ruled out by the broader balance of polling data, either: Leo, The Upshot’s Senate model, gives the Republicans a 68 percent chance of winning the chamber.
An earlier version of this article gave an imprecise figure for the number of respondents to the recent poll. It was nearly 100,000, not more than 80,000.