Mitt Romney clinched the Republican presidential nomination Tuesday with a win in the Texas primary, a triumph of endurance for a candidate who came up short four years ago and had to fight hard this year as voters flirted with a carousel of GOP rivals.
Romney surpassed the 1,144 delegates needed to win the nomination by securing at least 88 delegates in the Texas primary, according to the Associated Press count.
The former Massachusetts governor has reached the nomination milestone with a steady message of concern about the U.S. economy, a campaign organization that dwarfed those of his GOP foes and a fundraising operation second only to that of his Democratic opponent, President Obama.
"I am honored that Americans across the country have given their support to my candidacy, and I am humbled to have won enough delegates to become the Republican Party's 2012 presidential nominee," Romney said.
"Our party has come together with the goal of putting the failures of the last 3 1/2 years behind us. I have no illusions about the difficulties of the task before us. But whatever challenges lie ahead, we will settle for nothing less than getting America back on the path to full employment and prosperity."
Romney must now fire up conservatives who still doubt him while convincing swing voters that he can do a better job fixing the nation's struggling economy than Obama. In Obama, he faces a well-funded candidate with a proven campaign team in an election that will be influenced by the economy.
Romney went on the attack Tuesday, releasing a Web video citing the Obama administration's loan-guarantee investments in Solyndra and three other renewable-energy firms that lost money and laid off workers.
He spent Tuesday evening at a Las Vegas fundraiser with Donald Trump, who has been renewing discredited suggestions that Obama wasn't born in the United States. Romney says he believes Obama was born in America, but he has yet to condemn Trump's repeated insinuations to the contrary.
"If Mitt Romney lacks the backbone to stand up to a charlatan like Donald Trump because he's so concerned about lining his campaign's pockets, what does that say about the kind of president he would be?" Obama's deputy campaign manager, Stephanie Cutter, said.
Asked Monday about Trump's contentions, Romney said: "I don't agree with all the people who support me, and my guess is they don't all agree with everything I believe in." He added: "But I need to get 50.1 percent or more, and I'm appreciative to have the help of a lot of good people."
Trump told CNN in an interview Tuesday that he and Romney talk about other issues -- jobs, China, oil and more -- and not about Obama's birthplace or the validity of his birth certificate.
Asked how he viewed Romney's position that the president was born in the U.S., Trump said: "He's entitled to his opinion, and I think that's wonderful. I don't happen to share that opinion, and that's wonderful also."
Republicans won't officially nominate Romney until late August at the GOP National Convention in Tampa, Fla. Romney has 1,174 convention delegates.
He won at least 88 delegates in Texas with 64 left to be decided, according to early returns. The 152 delegates in Texas are awarded in proportion to the statewide vote.
Texas Republicans also voted in a Senate primary to choose a candidate to run for the seat being vacated by Sen. Kay Bailey Hutchison. Lt. Gov. David Dewhurst led in Tuesday's voting but fell short of the majority he needed to avoid a July runoff with state Solicitor General Ted Cruz. The nominee will be strongly favored to win in November in heavily Republican Texas.
Romney, 65, is clinching the presidential nomination later in the calendar than any recent Republican candidate -- but not quite as late as Obama in 2008. Obama clinched the Democratic nomination on June 3, 2008, at the end of an epic primary battle with Hillary Rodham Clinton. Four years ago, John McCain reached the threshold on March 4, after Romney had dropped out of the race about a month earlier.
This year's primary fight was extended by a back-loaded primary calendar, new GOP rules that generally awarded fewer delegates for winning a state and a Republican electorate that built up several other candidates before settling on Romney.
Texas Gov. Rick Perry, businessman Herman Cain, former House Speaker Newt Gingrich, former Sen. Rick Santorum of Pennsylvania and Trump all had sat atop the Republican field at some point. Rep. Michelle Bachmann of Minnesota peaked for a short time, too.
But Romney outlasted them, even as some GOP voters and tea party backers questioned his conservative credentials.
Romney has been in general-election mode for weeks, raising money and focusing on Obama, largely ignoring the primaries since his competitors dropped out or stopped campaigning. Santorum suspended his campaign April 10; Gingrich left the race a few weeks later.
Texas Rep. Ron Paul said on May 14 he would no longer compete in primaries.