In Arkansas, Democratic Sen. Blanche Lincoln struggles against a flood of labor money. In Nevada, Republican Sharron Angle is waging a Senate campaign that benefits from a conservative combination of the Tea Party Express and Club for Growth.
They are among the candidates as a dozen states hold primaries on Tuesday, picking party standard-bearers for Congress and governor for the fall in a campaign season marked by economic woe and political upheaval.
Two senators - including Arlen Specter (D., Pa.) - and two House members have been denied renomination in earlier races, one from each party in each house of Congress. Among Republicans, tea-party activists have changed the course of several other races to the consternation of the party's establishment.
In a year of danger for incumbents, Lincoln is the most prominent of those in trouble in the week's races. Regardless of the outcome in Arkansas, organized labor already claims victory.
By denying the two-term moderate Democrat a majority in the May 18 primary and forcing her into a runoff with Lt. Gov. Bill Halter, "We've been able to demonstrate that labor is unified around this campaign of accountability," said Jon Youngdahl, political director of the Service Employees International Union and a key strategist in organized labor's campaign to dump Lincoln. "It sends an important message to other members of Congress."
Youngdahl said Lincoln has supported free-trade legislation that unions oppose, and opposed an option for a government-run insurance option that labor wanted in this year's health-care legislation.
Records on file at the Federal Election Commission show organized labor has spent at least $5 million in recent weeks to defeat Lincoln.
In Nevada, Angle's primary path has been cleared not only by conservative organizations, but by a group partial to the Democratic incumbent, Senate Majority Leader Harry Reid.
Records show the Club for Growth and Tea Party Express have each spent nearly $500,000 to help Angle or suppress support for pre-race front-runner Sue Lowden. Businessman Danny Tarkanian is the third major contender in the race.
The Patriot Majority has spent an additional $300,000, much of it from unions, on television ads ridiculing Lowden for having suggested consumers barter chickens for health care. The group is run by a long-ago aide to Reid.
Nevada's Republican Gov. Jim Gibbons faces a difficult challenge for renomination after a term marked by a messy divorce.
Republicans in California could send two political neophytes, wealthy former business executives Meg Whitman and Carly Fiorina, into races to succeed Republican Gov. Arnold Schwarzenegger and challenge Democratic Sen. Barbara Boxer.
Whitman, a former eBay chief executive, has invested more than $70 million of her own fortune in the race against Steve Poizner, the state insurance commissioner and wealthy former businessman who has put $24 million into his campaign. The all-but-certain Democratic nominee is Attorney General Jerry Brown, who was governor in the 1970s and 1980s.
Fiorina, a former Hewlett Packard Co. chief executive, has a lead in polls over former U.S. Rep. Tom Campbell and State Assemblyman Chuck DeVore, a tea-party favorite. Boxer's campaign has depicted the Republicans as out of step with mainstream Californians.
In South Carolina, six-term Rep. Bob Inglis is trying to fend off Republican primary challengers who have made the race a referendum on his 2008 vote to bail out the nation's banking industry. South Carolina Republicans also are choosing from a field of four candidates hoping to succeed term-limited Republican Gov. Mark Sanford, who was damaged by his days-long absence from office during an extramarital affair with an Argentine woman.
Georgia, Maine, Iowa, Montana, New Jersey, North Dakota, South Dakota, and Virginia also hold primaries.
Multiple states besides New Jersey hold primary elections Tuesday. A look at key races among them:
Arkansas. Sen. Blanche Lincoln is trying to fend off Lt. Gov. Bill Halter in a Democratic runoff after neither drew 50 percent in the May 18 primary.
California. Republicans could nominate two political neophytes, wealthy former business executives Meg Whitman and Carly Fiorina, in statewide races. Whitman is seeking to succeed Gov. Arnold Schwarzenegger; Fiorina wants to challenge Sen. Barbara Boxer (D., Calif.). The Democrats' nominee for governor is all but certain to be Attorney General Jerry Brown, the former governor.
Nevada. Republicans including former state legislators Sharron Angle and Sue Lowden and businessman Danny Tarkanian are battling for the chance to take on Democratic Senate Majority Leader Harry Reid in the Nov. 2 election. And Nevada Republicans appear ready to punish Gov. Jim Gibbons for his messy divorce, potentially making him the first sitting governor to lose a nominating contest in the state in 100 years.
South Carolina. Rep. Bob Inglis tries to fend off challengers who have made the Republican primary a referendum on his 2008 vote to bail out the banking industry. Also, four candidates are vying for the GOP nomination for governor to succeed term-limited Republican Mark Sanford. State Rep. Nikki Haley has the backing of the tea party and Sarah Palin in her bid to become the state's first female governor.