Romney Finds Himself Upstaged by Trump on Big Day Mitt Romney and his wife, Ann, with Donald Trump in February in Las Vegas for an endorsement announcement. LAS VEGAS - It was supposed to be a day of triumph for Mitt Romney, when he would at last formally claim the Republican presidential nomination with a victory in the Texas primary. And Mr. Romney was to focus attention on an aggressive new attack on President Obama, highlighting the White House's role in backing failed companies like Solyndra. Instead, Tuesday was hijacked by Donald J. Trump. Inexplicably to many in his party, Mr. Romney had scheduled an appearance at a fund-raiser in Las Vegas on Tuesday night with Mr. Trump. And Mr. Trump, ever ready to seize the spotlight and toss rhetorical grenades, played to type in several interviews, repeating his doubts about the president's Hawaiian birth certificate. "A lot of people do not think it was an authentic certificate," Mr. Trump said in a combative interview with Wolf Blitzer on CNN. Now, you won't report it, Wolf, but many people do not think it was authentic. That and other statements left the Romney campaign to fend off questions about the candidate's views on that long-discredited accusation and whether he was willing to tolerate extreme views for his own political gain. During a brief conversation with reporters on Monday, before Mr. Trump's latest comments, Mr. Romney sought to compartmentalize Mr. Trump's fund-raising prowess as separate and apart from his conspiratorial accusations. "You know, 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 told reporters. But I need to get 50.1 percent or more, and I'm appreciative to have the help of a lot of good people. Aides to Mr. Romney said he does not question the president's birthplace. In an e-mail statement on Tuesday, Andrea Saul, a campaign spokeswoman, wrote, "Governor Romney has said repeatedly that he believes President Obama was born in the United States." But during campaign events on Tuesday, Mr. Romney showed little willingness to distance himself from Mr. Trump or address further questions. He broke from his recent practice of making himself available to reporters on his plane or on the rope line. He also canceled some interviews with local news media. Mr. Obama's campaign, meanwhile, seized upon Mr. Trump's comments, releasing a Web video on Tuesday morning that accused Mr. Romney of being unwilling to stand up to "voices of extremism." The video notes that during the 2008 presidential campaign, Senator John McCain of Arizona corrected extreme voices he encountered at town-hall-style meetings. "Why won't Mitt Romney do the same?" the video asks as it plays snippets of Mr. Trump questioning the president's birthplace. This is not the first time Mr. Romney has been criticized for not taking a strong enough stance on a controversial issue. In March, he was asked to comment on Sandra Fluke, a law school student who was called a "slut" and a "prostitute" by the radio host Rush Limbaugh after she testified before Congress in favor of employers" covering birth control for all women. Mr. Romney said of Mr. Limbaugh's remarks, "It's not the language I would have used." And at a town-hall-style meeting this month, Mr. Romney at first did not offer a public rebuke of a female supporter who stood and said Mr. Obama "should be tried for treason." He later clarified to reporters on the rope line that he did not agree with the woman's remarks. With Mr. Trump, the Romney campaign privately maintains an attitude of quiet exasperation and good-natured eye-rolling, but it is reluctant to criticize him publicly. He is a prolific fund-raiser and willing surrogate whose fame and following can marshal both top-dollar and small-money donors. In April, Mr. Trump hauled in $600,000 at a fund-raiser celebrating Ann Romney's birthday. And the campaign is raffling off a fantasy day with Mr. Trump, with tickets starting at $3, as part of its effort to raise $300,000 in small donations. The fund-raiser in Las Vegas, expected to bring in $2 million, was on Mr. Romney's schedule before Mr. Trump was associated with it as part of a Western swing that includes two fund-raising events on Wednesday in California and meetings with other supporters and officials (among them, Sheldon Adelson, the billionaire casino owner and Republican donor with whom Mr. Romney ate lunch on Tuesday). Reporting was contributed by Michael D. Shear from Washington, Nicholas Confessore from New York and Michael Barbaro from Las Vegas.