Two Republican stalwarts in Indiana fought their way onto the November ballot as former Sen. Dan Coats won the GOP primary to reclaim his old seat and 14-term Rep. Dan Burton barely survived against a slew of strong challengers in the state's 5th District.
Mr. Coats, seeking to win the seat he ceded to retiring Democrat Evan Bayh 12 years ago, now faces Democratic Rep. Brad Ellsworth in what is likely one of the most spirited Senate contests this fall.
Indiana, North Carolina and Ohio all held primaries Tuesday to kick off what will be a busy month of races to set the table for November's races, in which increasingly confident Republicans hope to make a run at the Democratic majorities in both houses of Congress.
In other marquee races, Ohio Democratic Lt. Gov. Lee Fisher defeated state Secretary of State Jennifer Brunner for the right to take on Republican former Rep. Rob Portman for another open Senate seat, that of retiring GOP Sen. George V. Voinovich.
And in North Carolina, Democrats Elaine Marshall, the state secretary of state, and Cal Cunningham, an Iraq war veteran, were headed for a June 22 run-off after Ms. Marshall just failed to reach the 40 percent threshold to claim the nomination outright. The winner faces first-term Republican Sen. Richard Burr.
Mr. Coats, after serving 10 years as a senator, left office in 1998 and moved to Virginia, where he has worked as a lobbyist. He also bought a home in North Carolina with the intent of retiring there, prompting critics to label him a carpetbagger for seeking a Senate seat from the Hoosier state once again.
All four of his challengers have accused him of being a Washington insider and moderate. His strongest rivals, former Rep. John Hostettler and state Sen. Marlin Stutzman, both enjoyed strong support from conservatives.
Mr. Burton won with barely a third of the vote as his opponents split the anti-incumbent vote. Just behind Mr. Burton was former Indiana Republican Party Executive Director Luke Messer. Another embattled GOP incumbent, Rep. Mark E. Souder, also survived a primary challenge from well-heeled car dealer Bob Thomas in his 3rd District.
The Tuesday primaries usher in a busy May election season. Nebraska and West Virginia voters go to the polls May 11, followed by Arkansas, Kentucky, Pennsylvania and Oregon May 18. Idaho caps off the month with its May 25 primary.
Mr. Souder's victory is likely to be closely analyzed as a gauge of the sentiment of GOP voters for Republican lawmakers who backed the 2008 bank bailout bill.
"This may be the only case, period, where [the bailout] really costs a member their seat this year," said David Wasserman, who covers House races for the Cook Political Report. "This is the first Republican primary that [Mr. Souder] has had to face for that vote, and northeast Indiana has some of the worst unemployment in the country."
Mr. Burton's difficulties were surprising in light of his 66 percent romp in his 2008 general election race, but he had also faced a tough primary challenge two years ago.
The Indianapolis Star, the district's largest newspaper, didn't make a primary endorsement. But in an editorial last week headlined "Challengers better than Burton," the paper said the slate of challengers all "would be a significant improvement over the incumbent."
In swing-state Ohio, the retirement of Mr. Voinovich has set off one of the most competitive and unpredictable Senate races this year.
Mr. Portman, who also was President George W. Bush's budget chief, ran unchallenged in the Republican primary. Ms. Brunner was a favorite of the left, but Mr. Fisher had the fundraising advantage and used it to wrest a convincing victory in the Democratic primary in the end.
As in Indiana, the general election in Ohio is shaping up to be one of the toughest Senate races in the nation, as most polling services rate it too close to call.
• Valerie Richardson contributed to this article.