WASHINGTON — Six-term Indiana Sen. Richard Lugar was routed by the right flank of his own Republican Party, and North Carolina voters decided overwhelmingly Tuesday to strengthen their state’s gay marriage ban. It was a conservative show of enthusiasm and strength six months before the nation chooses between Democratic President Obama and GOP challenger Mitt Romney.

Romney swept three Republican primaries Tuesday, moving ever closer to sealing his nomination.

“I have no regrets about running for re-election, even if doing so can be a very daunting task,” the 80-year-old Lugar said as he conceded to the tea party-backed GOP opponent who ended his nearly four-decade career in the Senate. Lugar’s foe, state Treasurer Richard Mourdock, had painted the Republican senator as too moderate for the conservative 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.”

North Carolinians voted to amend their state constitution to define marriage as between one man and one woman, effectively outlawing gay unions.

The contests overshadowed Romney’s continued progress toward the GOP presidential nomination. He won the GOP presidential primaries in Indiana, North Carolina and West Virginia, drawing close to the 1,144 delegates he needs to clinch the nomination. He was likely to win 100 or so delegates of the 288 he still needed.

Even Romney, the former Massachusetts governor, was essentially ignoring the primaries. He spent the day campaigning in Michigan, where he castigated Obama as an “old-school liberal” whose policies would take the country backward.

The outcomes of Tuesday’s far-flung voting gave clues about the state of the electorate — and highlighted the political minefields facing both Republican and Democratic candidates — with the presidential contest well under way.

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 Obama to publicly support same-sex unions before November.

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