West Virginia Democratic Rep. Alan Mollohan lost his bid for a 15th term tonight at the hands of state Sen. Mike Oliverio, a defeat that further affirms the anti-incumbent sentiment coursing through the country.

NUMBER 2: BLANCHE LINCOLN OF ARKANSAS is facing a challenge from her own party as well as an impressive line-up of Republicans…..stay tuned

NUMBER 3: HOORAY FOR SENATOR MITCH McCONNEL who is not backing Rand Paul in Kentucky but is backing Trey Grayson as really good candidate….

By PETER WALLSTEN

The country’s churlish political mood has managed to give top Democrats and Republicans at least one common goal—hustling to keep an anti-Washington wave from washing their preferred candidates out of next week’s primary elections.

President Barack Obama appears in an advertisement that began airing Tuesday in support of Sen. Arlen Specter, the Pennsylvania Democrat who trails his primary opponent in several polls.

Mr. Obama has also taped an ad for Arkansas Sen. Blanche Lincoln, who also faces a stiff challenge from Democratic activists on the political left. Both elections will be held on Tuesday.

The Republican Senate leader, Mitch McConnell of Kentucky, is working to shore up the candidacy of Senate contender Trey Grayson, Kentucky’s secretary of state, who trails political rookie Rand Paul in many polls. Mr. McConnell is featured in a new television ad, automated phone calls and a mailing for Mr. Grayson.

Polling across the country shows that many voters in both parties disagree with their party leaders’ choices of who should carry the mantle in November’s general elections.

That has created an unusual dynamic in which Messrs. Obama and McConnell find themselves going against the wishes of many of their own core supporters.

Another Republican with official party backing, Sen. Robert Bennett of Utah, lost his renomination fight at a state party convention Saturday to two candidates with ties to the tea-party movement.

But the challenges to Mr. Specter and Ms. Lincoln show that the insurgent mood is cresting on both sides of the aisle.

A Democratic casualty came Tuesday night in West Virginia as primary voters denied U.S. Rep. Alan Mollohan a 15th term, opting instead for a state senator to be the party’s nominee.

“Both parties are wrestling with the great voter discontent with government,” said Andrew Kohut, president of the Pew Research center.

A new Pew poll turned up signs of the unease, as just 43% of those surveyed wanted to see their own representative to Congress win re-election—the lowest mark in 20 years of asking the question, Mr. Kohut said.

The question facing party officials is how the agitated mood among primary voters, who tend to be both more motivated and ideological, will affect each party’s ability to win general elections, in which centrist voters traditionally hold sway.

The success so far of Mr. Paul’s campaign in Kentucky shows a hunger in the party base for a strongly ideological message, said Kentucky GOP Chairman Steve Robertson, who is neutral in the race.

He said Mr. McConnell is popular and that Mr. Grayson is well-liked, but GOP voters like the “red meat” anti-Washington rhetoric being dished out by Mr. Paul.

In a new TV ad, Mr. McConnell, looking into the camera, says that he rarely endorses in primaries, but that “these are critical times.”

Mr. McConnell says, “I know Trey Grayson and trust him,” and lauds the candidate’s “conservative leadership.”

The ad flashes images of other prominent Republicans backing Mr. Grayson, including former Vice President Dick Cheney, former New York Mayor Rudy Giuliani and former Pennsylvania Sen. Rick Santorum.

Asked about the risk of tying Mr. Grayson too closely to Washington, campaign spokesman Nate Hodson said: “Our polling shows that Sen. Mitch McConnell is the most popular Republican in Kentucky.”

In Pennsylvania, state party leaders, who are backing Mr. Specter, have argued that the incumbent senator is the Democrats’ best hope of keeping the seat this fall.

“At the end of the day, the threshold question is who can win in November,” said state party chairman T.J. Rooney, who is backing Mr. Specter.

The senator is embracing the establishment label. His new advertisement uses footage from an appearance with Mr. Obama last fall in which the president praised Mr. Specter for backing the federal economic-stimulus package. “I love Arlen Specter,” Mr. Obama declares. Vice President Joe Biden plans to campaign for Mr. Specter in the coming days.

In associating himself with top party leaders, Mr. Specter is trying to counter charges from his rival, U.S. Rep. Joe Sestak, that he isn’t a genuine Democrat. Mr. Specter joined the Democratic Party last year after polls showed him likely to lose the GOP primary to a conservative challenger.

A new ad from Mr. Sestak shows footage of former President George W. Bush campaigning for Mr. Specter.

A spokesman for Mr. Specter, Chris Nicholas, said the campaign was “aware of the mood” of the voters, but that support from the party machinery was nonetheless beneficial.

More high-level divisions are apparent in Arkansas, where labor unions are pouring millions of dollars into the state to boost Lt. Gov. Bill Halter’s primary challenge to Ms. Lincoln.

Support for Ms. Lincoln by top Democratic officials has taken a lower profile, with the president cutting a radio ad in recent days aimed at African-Americans and other “surge voters” who backed him in 2008.

Lincoln spokesman Charlie Gocio said the senator was proud to have the president’s support. But he said her record “shows she is an independent voice that answers only to Arkansas.”

Write to Peter Wallsten at peter.wallsten@wsj.com