"For everyone who has been counted out but refused to be knocked out, for everyone who has stumbled but stood right back up and for everyone who works hard and never gives up — this one is for you," she said.
She said she had demonstrated her potential strength in the general election by winning primaries in the big states Democrats will count on in the fall — among them California, New York, New Jersey and now Ohio.
In the exit polls, however, a majority of voters in Texas and Ohio said Obama was more likely to beat the Republican nominee in the fall.
Even so, a barrage of Clinton attacks on Obama apparently resonated with voters. During the past week, she questioned his ties to indicted Chicago developer Tony Rezko, the sincerity of his opposition to NAFTA, his readiness to serve as commander-in-chief and his ability to deliver solutions as well as soaring rhetoric.
In Texas, Clinton won by nearly 2-1 among those who decided whom to vote for within three days of the election. She carried late-deciding Ohioans by double digits.
Not conservative enough
Despite his success Tuesday, McCain continued to struggle to convince the GOP's conservative base to embrace his candidacy.
About one-third of Republican voters in Texas and Ohio called themselves "very conservative." Those voters supported Huckabee — in Ohio by nearly 20 points. At least 40% of GOP voters in Texas and Ohio said McCain wasn't conservative enough.
Even so, seven in 10 Republicans said they would be satisfied with McCain as the nominee, numbers equal to or better than those for Clinton and Obama in the Democratic exit polls in those two states.
McCain began the night with 1,014 delegates by the AP count, 177 short of the number needed for nomination.
He picked up 89 delegates in Texas and 17 in Vermont, as well as at least 58 in Ohio and nine in Rhode Island — enough to put him over the top. At his victory rally in Dallas was a banner with the magic number needed for the GOP nomination — 1,191 — as a backdrop.
Speaking to supporters there, McCain claimed the nomination and said he would "make a respectful, determined and convincing case to the American people that our campaign and my election as president, given the alternatives presented by our friends in the other party, are in the best interests of the country we love."
The audience applauded when McCain pledged to "defend the decision to destroy Saddam Hussein's regime" and invade Iraq, though he criticized "the failed tactics that were employed for too long."
He offered a somewhat different emphasis than he has in the past on the war, indicating he wanted to withdraw U.S. troops as soon as a series of conditions could be met.
"The next president must explain how he or she intends to bring that war to the swiftest possible conclusion without exacerbating a sectarian conflict that could quickly descend into genocide; destabilizing the entire Middle East; enabling our adversaries in the region to extend their influence and undermine our security there; and emboldening terrorists to attack us elsewhere with weapons we dare not allow them to possess," McCain said.
At a smaller rally a few miles away, Huckabee already had dropped his presidential bid, joking about his low-budget campaign.