[cnn-photo-caption image=http://i.cdn.turner.com/cnn/2008/POLITICS/03/04/march.4.contests/t1land.mccain.wave.ap.jpg caption="Sen. John McCain clinched the GOP presidential nomination Tuesday, according to CNN projections."]
DALLAS, Texas (CNN) - Sen. John McCain accepted the mantle of presumptive GOP nominee for president, thanking his supporters in Rhode Island, Texas, Ohio and Vermont - states he won Tuesday night to take him over the top in delegates.
"I am very, very grateful and pleased to note that tonight, my friends, we have won enough delegates to claim with confidence, humility and a great sense of responsibility, that I will be the Republican nominee for president of the United States," the Arizona senator said.
Former Arkansas Gov. Mike Huckabee quit the presidential race after it became clear that McCain would win the Republican nomination, after winning Tuesday's GOP primaries.
"It's now important that we turn our attention not to what could have been or what we wanted to have been, but now what must be - and that is a united party," Huckabee told supporters in Dallas, Texas, after losing Tuesday's primary in Texas and three other states.
Huckabee, a former Baptist pastor, thanked volunteers for "keeping the faith" and told them, "I'd rather lose an election than lose the principles that got me into politics in the first place."
"Tonight, I hope that our battle was never about us," he said. "It was about our country and our liberty. And now we join with Sen. McCain and the rest of our party to continue that battle."
Huckabee drew first blood in the GOP race, winning the January 3 Iowa caucuses, and won several Deep South states in the February 5 "Super Tuesday" contests. But he struggled to gain traction outside the region, while McCain won big states like New York and California handily and swept Tuesday's contests in Texas, Ohio, Rhode Island and Vermont.
Huckabee's exit leaves anti-war Texas congressman Ron Paul, a former Libertarian presidential candidate, as McCain's sole remaining opponent.
McCain's campaign - his second run for the White House - was largely written off for dead last summer amid outspoken opposition from the party's conservative base, a major staff shakeup and disappointing fund-raising.