Six years after becoming his party's nominee for vice president, Democratic Senator Joe Lieberman faces a struggle to keep his Senate seat in Tuesday's primary against an anti-war challenger.
In Georgia, Congresswoman Cynthia McKinney, who made headlines this year for a scuffle with a U.S. Capitol Police officer, is locked in a runoff for her district's Democratic nomination.
Primaries are also being held Tuesday in Colorado, Missouri and Michigan.
Lieberman's seat was the biggest prize at stake. The three-term senator, nationally known for his centrist views, faces harsh criticism in his home state for supporting the Iraq war and has been labeled by some Democrats as too close to Republicans and President Bush.
Challenger Ned Lamont, a millionaire owner of a cable television company, held a slight lead of 51 percent to 45 percent over Lieberman among likely Democratic voters heading into Tuesday's primary.
Lieberman has tried to persuade voters that he is still a true Democrat and says Lamont will need "training wheels" should he ultimately win the general election.
In Georgia, McKinney is trying to counter her opponent's charge that the six-term congresswoman is "the candidate of polarization and divisiveness."
McKinney, the state's first black woman in Congress, once claimed the Bush administration had advance knowledge of the Sept. 11, 2001, terror attacks. In March, she struck a Capitol Police officer who did not recognize her and tried to stop her from entering a House office building. A grand jury in Washington declined to indict her, but she was forced to apologize in the full House.
In other primaries Tuesday:
— In Colorado, voters will choose among six Republican candidates to succeed retiring Republican Rep. Joel Hefley, a 10-year veteran. The winner will face Democratic Air Force veteran Jay Fawcett. In another race, three Democrats are competing to replace Congressman Bob Beauprez, the Republican nominee for governor.
— In Michigan, Republican Rep. Joe Schwarz faces a serious challenge from former state lawmaker Tim Walberg. Schwarz, a moderate Republican, is backed by Bush, Arizona Sen. John McCain and the National Rifle Association.
— Missouri Republican Sen. Jim Talent and Democratic challenger Claire McCaskill, the state auditor, are expected to win their party's primaries. Voters will also decide whether to renew a 22-year-old sales tax to fund state parks and other conservation initiatives.