McCain, who is trying to court conservatives unhappy with his record on taxes, immigration and his opposition to a federal ban on same-sex marriage, battled back Huckabee in Virginia, where a high turnout of Christian evangelicals and conservatives made it a tight race.
Thirty-four percent of Republican primary voters in Virginia described themselves as very conservative, putting Huckabee in the game, reports ABC News' Gary Langer.
He won very conservative voters over McCain by better than a 3-1 margin, while McCain narrowly prevailed among somewhat conservatives and won moderate Republicans by more than 2-1, according to exit polls.
McCain, who had an insurmountable delegate lead going into today's primaries, has picked up hundreds more delegates thanks to Virginia and Washington, D.C.'s winner-take-all rules.
Despite his continued losses, Huckabee vowed again tonight not to pull the trigger on his campaign until someone reaches the 1,191 GOP delegates needed to win the Republican nomination.
"The nomination is not secured until someone has 1,191 delegates," Huckabee said at a news conference in Little Rock, Arkansas tonight.
"It would be premature to quit to quit the game," he said. "I've not been one who believes you believe the field because it has gotten difficult. You keep playing last second of the clock."
McCain's campaign tonight said Huckabee was on a losing quest.
"After tonight it is mathematically impossible for Governor Huckabee to secure the nomination," McCain communicators director Jill Hazelbaker told ABC News' Ron Claiborne.
In his victory speech tonight, McCain appeared to deliver a message to those conservatives who doubt him.
"As I have done my entire career, I will make my case to every American who will listen," McCain said. "I will not confine myself to the comfort of speaking only to those who agree with me ... I will fight every moment of every day for what I believe is right for this country, and I will not yield."
Despite freezing temperatures, rain and sleet in some areas, Democrats energized by historic candidates and the tighest nominating race in recent history turned out in high numbers.
"I voted for the next president of the United States, Barack Obama," said Phil Andonian, a 31-year-old lawyer sporting a Barack Obama T-shirt underneath his winter coat, outside a polling station in the nation's capital.
"The Clintons have shown themselves to be a political machine not much different than the Bush administration," Andonian said. "I think Obama is the one to bring about the kind of change we need in Washington."
Walking home from the elementary school where he voted, a 75-year old African-American man reflected on his vote for Obama.
"It's historic," he said, declining to give his name. "And this is probably the last time I'm gonna get to vote."
In recent days Clinton's campaign has downplayed the importance of today's primary contests, focusing instead on the delegate-rich states of Ohio and Texas voting March 4 and Pennsylvania, which votes April 22.
Today Clinton kept a low profile, visiting her campaign headquarters in Virginia and doing satellite television interviews, looking beyond Tuesday's trio of contests and touting the importance of a March 4 vote in Ohio.