WASHINGTON (AP) — In a show of conservative enthusiasm, a tea-party backed Republican vanquished six-term Indiana Sen. Richard Lugar in a GOP primary and North Carolina voters decided overwhelmingly to strengthen their state's gay marriage ban.

Republican Mitt Romney, who long has been viewed skeptically by the GOP's base, won three primaries to move closer to clinching the nomination of a party that remains sharply divided between its establishment and right flanks.

The nation's polarized environment was on display in Tuesday contests scattered across several states six months before Americans choose whether to give Democratic President Barack Obama another four years.

That was especially true in Lugar's unsuccessful effort to beat back a challenge from Indiana Treasurer Richard Mourdock, who had painted the Republican senator as too moderate for the conservative state.

"We are experiencing deep political divisions in our society right now. These divisions have stalemated progress in critical areas," Lugar, a Capitol Hill diplomat and a deal-maker, said after an election that marked an end to a nearly four-decade career in the Senate.

Elsewhere, North Carolinians voted to amend their state constitution to define marriage as between one man and one woman, effectively outlawing gay unions through a ballot measure pursued by the right.

Wisconsin Democrats overwhelmingly picked Milwaukee Mayor Tom Barrett to challenge Republican Gov. Scott Walker in a June recall election. The primary outcome set up a re-match; Barrett lost to Walker in 2010.

The highly charged and hard-fought contests overshadowed Romney's continued progress toward the GOP presidential nomination. He won Republican presidential primaries in Indiana, North Carolina and West Virginia, drawing close to the 1,144 delegates he needs to clinch the nomination. He won at least 63 delegates, with 28 from West Virginia still undecided. He had 919 delegates, 225 shy of what he needs to become the nominee.

The results of Tuesday's far-flung voting gave clues about the state of the electorate — and illustrated the political minefields facing both Republican and Democratic candidates — with the presidential contest well under way. The results were a warning to incumbents. They also highlighted tea party enthusiasm. And, in one state at least, they indicated that wedge issues are still a force even with an electorate focused on economic concerns.

There also was an indication of just how unpopular Obama is in some parts of the country: A man in prison in Texas was getting 4 out of 10 votes in West Virginia's Democratic presidential primary.

Within minutes of Lugar's loss, Democrats were painting Mourdock as too extreme for the state.

Tea party groups were crowing about the win, and Mourdock urged supporters to donate to his general election campaign, saying, "We left everything on the table to win the primary." He will face Democratic Rep. Joe Donnelly in November.

Republicans need to gain four seats to take control of the Senate, and Lugar's loss "gives Democrats a pickup opportunity," said Sen. Chuck Schumer, D-N.Y.

Playing out in a conservative state, the race illustrated the electorate's animosity toward many incumbents and anyone with deep ties to Washington. That was clear when Lugar, who hasn't faced questions about his residency in decades, found himself on the defensive over whether he lived in Indiana or northern Virginia. Lugar also was cast as too moderate for the conservative GOP in Indiana, and he took heat for his work with Democrats on issues such as nuclear nonproliferation, underscoring deep polarization in the country as well as a split in the GOP between the establishment wing and the insurgent tea party.

In a statement, Obama praised his former Senate colleague as someone "who was often willing to reach across the aisle and get things done."

The Mourdock vs. Donnelly match-up could develop into a hotly contested race with the potential to affect the White House contest.

Obama carried Indiana in 2008, partly because of his ties to the populous northwestern part of the state neighboring his hometown of Chicago. Democrats acknowledge it will be difficult to win Indiana again this year. Still, the state could become more hospitable to Obama if the Democrats, believing they have a better chance with Lugar out of the race, spend heavily to compete against Mourdock. The state now is on the Obama team's watch list.

In North Carolina, voters moved in the opposite direction from a string of states — Democratic-leaning places such as New York and Vermont as well as conservative Iowa — where same-sex marriage is now legal. Six states and Washington, D.C., now recognize gay unions.

North Carolina law already bans gay marriage, but the amendment on the state ballot effectively slammed that door.

In the days before the North Carolina vote, two top administration officials — Vice President Joe Biden and Education Secretary Arne Duncan — expressed support for gay marriage. Obama supports most gay rights but has stopped short of backing gay marriage.

The Biden and Duncan comments sent the White House into damage-control mode as gay rights advocates pressed for him to publicly support same-sex unions before November. Aides also tried to use the focus on the issue to criticize Romney's equivocations on gay rights over the years.

Obama's campaign said Tuesday that the president was "disappointed" with the state's amendment. Obama's spokesman for North Carolina, Cameron French, called the measure "divisive and discriminatory."

Romney, in turn, has emphasized his position that marriage should be solely between one man and one woman. He has said he supports a federal constitutional amendment banning same-sex marriage.

In Wisconsin, voters chose Barrett — one of four Democrats on the ballot — to challenge Walker in the June 5 recall election.

Union rights are dominating the recall. Walker effectively ended collective bargaining rights for most state workers and since then has emerged as a national conservative hero. The recall effort, mounted by opponents of his actions, has dominated the state political landscape — even overshadowing Romney's primary victory there, which essentially ended the nomination fight.