Left, right brace for voters’ anti-incumbent anger

“There are seats [nationwide] where Democrats absolutely will be hurt by votes for health care or cap-and-trade [emissions trading programs] … so that was a smart set of positions for Critz to take,” said John Fortier, a political specialist with the American Enterprise Institute, a conservative-leaning think tank. “It wouldn’t surprise me that in a number of individual races you’ll see that.”

Several pundits suggested that Tuesday’s results were more a rejection of Mr. Obama than of Washington or incumbents. Mr. Obama supported both Mr. Specter and Sen. Blanche Lincoln, a Democrat who was forced into a runoff in Arkansas by a challenger from the left, Lt. Gov. Bill Halter.

Those two will face off for the Democratic Party’s Senate nomination on June 8 - and whoever wins then faces an uphill battle in the fall against the GOP nominee, Rep. John Boozman, who holds a decisive lead in the polls over either Democrat.

Other analysts warn of reading too much into Mr. Obama’s support of the incumbent senators. Mr. Specter, who only last year bolted the Republican Party to become a Democrat, is seen as a turncoat by many Democratic voters. White House support for Mr. Specter was tepid, with the president deciding against visiting Pennsylvania in recent weeks on behalf of the incumbent.

“If I were the president, I wouldn’t be too alarmed by what happened in Pennsylvania because you have a very attractive younger [challenger] who has been a Democrat all his life,” said Karlyn Bowman of the American Enterprise Institute.

In Arkansas, a surprisingly strong show of support by organized labor helped push Mr. Halter into the runoff.

“And with Arkansas, a president almost has to endorse the incumbent,” Mr. Fortier said.

White House officials said the president didn’t watch the election results closely, but Tuesday’s setbacks follow earlier losses for Obama-backed candidates in races in Virginia, Massachusetts and New Jersey.

But overall, presidential endorsements generally have little impact in swaying the results of congressional elections, many analysts say.

“Presidents are great at raising money for candidates, but they really don’t have a lot of coattails when they go out and campaign for people, so I think it’s a little hard to say you can pin these losses directly on the administration’s doorstep,” said Michael D. Tanner, a political analyst with the Cato Institute, a libertarian think tank.

Mr. Tanner added, however, that a major reason for so much nervousness among voters “is because the administration’s policies have upset people.”

“There’s always a sort of anti-party-in-power dynamic [during midterms], but the level of anger here in both parties” is higher than usual, he said.

• Sean Lengell contributed to this article, which is based in part on wire service reports.