Six years after Democrats backed him for vice president, Sen. Joe Lieberman struggled to overcome a tough challenge in Tuesday's primary and escape retribution from his own party for supporting the Iraq war.

In Georgia, Rep. Cynthia McKinney, the fiery congresswoman who scuffled with a U.S. Capitol police officer earlier this year, was locked in a runoff for the Democratic nomination. Elsewhere, voters in Colorado, Missouri and Michigan also chose candidates for the fall elections.

The Connecticut Senate race has dominated the political landscape in recent weeks, and its outcome promises to echo through the fall.

The campaign of political novice Ned Lamont demonstrated the vehemence of anti-war sentiment among Democrats. Lamont is the millionaire owner of a cable television company whose time in politics has been limited to serving as a town selectman and member of the town tax board.

Yet he brought himself to the brink of defeating three-term incumbent Lieberman, the Democrats' vice presidential candidate in 2000. It was also a race watched closely by the liberal, Internet-savvy Democrats who lead the party's emerging "netroots" movement, groups such as Moveon.org that played a big role in pushing Lamont's candidacy.

A week ago, polls showed Lieberman trailing Lamont by more than 8 percentage points. The latest polls showed the race tightening, with Lamont holding a slight lead of 51 percent to 45 percent over Lieberman among likely Democratic voters, according to a Quinnipiac University poll released Monday.

The telephone poll of 784 likely Democratic primary voters, conducted from July 31 to Aug. 6, has a sampling error margin of plus or minus 3.5 percentage points.

Democratic critics targeted Lieberman for his strong support for the Iraq war and for his close ties to President Bush. They played and replayed video of the kiss President Bush planted on Lieberman's cheek after the 2005 State of the Union address.

Lieberman has said he will run as an independent in the fall if defeated in the primary. His falling poll numbers spurred some Democratic colleagues to make last-minute campaign appearances, including former President Clinton, Sen. Barbara Boxer of California and others.

On the final day of the race, Lieberman accused his opponent's supporters of hacking his campaign Web site and e-mail system. Campaign manager Sean Smith said the site began having problems Monday night and crashed for good at 7 a.m., denying voters information about the candidate.

"It is a deliberate attempt to disenfranchise voters," Smith said.

Lamont, campaigning early Tuesday afternoon in Bridgeport, said he knew nothing about the accusations. "It's just another scurrilous charge," he said.

In the lead up to Tuesday's primary, 14,000 new Connecticut voters registered as Democrats, while another 14,000 state voters switched their registration from unaffiliated to Democrat to vote in the primary.

In Georgia, McKinney, her state's first black congresswoman, is in a runoff in her bid for a seventh term. In the heavily Democratic district, the runoff winner is likely to win in the fall.

She has long been controversial, once suggesting the Bush administration had advance knowledge of the Sept. 11, 2001, terror attacks. Her comments helped galvanize opposition and she lost her seat in 2002, but won it again two years ago.

In her latest brouhaha 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 before the House. She drew less than 50 percent of the vote in last month's primary and faces off against Hank Johnson, the black former commissioner of DeKalb County, which encompasses much of Atlanta.

In other primaries Tuesday:

• In Michigan, Republican Rep. Joe Schwarz, a moderate who supports abortion rights, faces a vigorous challenge from conservative Tim Walberg, a former state lawmaker. The race has drawn more than $1 million from outside groups; Schwarz has received support from President Bush and Arizona Sen. John McCain.

• In Colorado, two open congressional seats have drawn crowds of candidates.

• Missouri Republican Sen. Jim Talent and Democratic challenger Claire McCaskill, the state auditor, are expected to win their party's primaries.