Unlike 2010, when the big story was the epic gains of Republicans in the House, this year's midterms will mostly be about the Senate. And this summer has been unkind to Democrats hoping to keep the upper chamber.
Two weeks ago the New York Times reported that Montana Democrat John Walsh plagiarized much of his 2007 Army War College master's thesis. Montana's two largest papers have called for him to end his campaign; one suggested he resign the Senate seat he was appointed to in February to complete the term of Max Baucus, who became ambassador to China.
Even before the plagiarism story broke, Republican Congressman Steve Daines had a double-digit lead. Now Democrats are unlikely to win even if Majority Leader Harry Reid forces Mr. Walsh to resign by the Monday deadline for replacing him on the ballot.
In Logan, W.Va, on Saturday, a coal miner asked Democratic hopeful Natalie Tennant why she supported President Obama. She didn't have a good answer. Her campaign chairman awkwardly explained that "because on most of his policies and stuff she supports" the president. The campaign later said he misspoke, but the damage was done.
In states where Mr. Obama is unpopular, candidates are tempted to distance themselves. This makes them look shifty and disloyal and could alienate the president's supporters. But not separating themselves can be lethal. Not one to let up, Republican Shelley Moore Capito will take advantage of Ms. Tennant's predicament.
Democrats are also faltering in two states they hoped to pick up. In Kentucky, Alison Lundergan Grimes declared on July 29 that, "The Iron Dome has been a big reason why Israel has been able to withstand the terrorists that have tried to tunnel their way in." But Iron Dome is a missile defense system and useless against the tunnels built by Hamas. This adds to existing questions about her command of the issues.
In Georgia, Democrat Michelle Nunn suffered a self-inflicted wound when it turned out that in December her campaign posted online a 144-page strategy memo. It suggested that she came across as "a lightweight" and "not a real Georgian," listing as weaknesses her support for ObamaCare and her vulnerability to being depicted as "a rubber stamp for Democrats." And Georgia's GOP runoff yielded a Republican, businessman David Perdue, who can win.
Nationally, Mr. Obama's job approval rating remains dangerously low—41% in Wednesday's Gallup tracking, 4% less than at this point in 2010. He is in worse shape on major issues. In the June 1 ABC News/Washington Post survey, the president's approval rating on immigration is 38%, down 10 points from April 2009. An Aug. 3 NBC News/Wall Street Journal poll put his approval rating on foreign affairs at 36% and on the economy at 42%, both down from 56% shortly after his 2009 inauguration.
Will Republicans coast to a Senate victory? On July 15, the Washington Post Election Lab gave Republicans an 86% likelihood of taking the Senate. This week Nate Silver of FiveThirtyEight rated the GOP's chances "in the neighborhood of 60-40," the same percentage as the New York Times and CBS concluded from their July 27 YouGov survey.
This is good news for the GOP, but Republicans shouldn't pop the champagne corks. It is early. There are too few nonpartisan surveys. Pollsters are still working to understand the impact of the increasing number of cellphone-only households.
The YouGov panel of online respondents allows the pollsters to use big samples at a low cost. But Jan van Lohuizen of Voter Consumer Research, a GOP polling firm, cautions YouGov's panel is not a random selection and is less reliable in smaller states that dominate this midterm election.
Another issue is money. Although Republicans have recently been doing better at fundraising in the 14 Democratic seats most at risk, Democratic candidates still had $58.2 million cash on June 30, compared with the GOP candidates' $35.9 million.
Then there's voter intensity. The Pew Research Centerasks voters if they are more enthusiastic than usual about voting than in prior congressional elections. In June 2010 Republicans had a 13-point advantage over Democrats (55% to 42%). Last month the GOP had an 8-point lead (45% to 37%). This explains Mr. Obama's strategy of division: Believing he can't persuade independents, he hopes to whip his left-wing base into a frenzy emphasizing especially cultural issues like abortion and contraception.
While the political topography favors the GOP and several Democratic candidates have been hurt in recent weeks, the battle for Senate control is far from over. Republicans who think otherwise are fooling themselves.
A version of this article appeared August 7, 2014, in the U.S. edition of The Wall Street Journal, with the headline How The Senate Races Are Breaking and online at WSJ.com.