No. They are worried that Trump isn’t a Republican Lindsey Graham Senator Lindsey Graham of South Carolina, who was one of the 16 other Republicans to run for president and has criticized Mr. Trump in the past, said Friday that he could not support him. “I just really believe that the Republican Party has been conned here, and this guy is not a reliable conservative Republican,” he told CNN’s Dana Bash. Previously, the only other Republican member of Congress who had come out as strongly against Mr. Trump was Senator Ben Sasse of Nebraska, who favors a third-party conservative candidate.

Not yet. They want to protect current party positions Paul D. Ryan Speaker Paul D. Ryan, the party’s leader in the House, said Thursday that he was “not ready” to endorse Mr. Trump and that it was up to the presumptive nominee to prove that he shares the party’s values. Mr. Ryan has serious policy differences with Mr. Trump, and he wants to protect the Republican majority in the House as well as his own political future, which could possibly include a run for president. The speaker’s announcement essentially gives permission to other Republican lawmakers to take a similar position, leaving room for them to distinguish themselves from the nominee.

Maybe. They are worried about their own elections Kelly Ayotte Senator Kelly Ayotte of New Hampshire, who faces a tough re-election this year, said she would “support the nominee” but not “endorse anyone this cycle,” an ambiguous position echoed by other lawmakers. Vulnerable House Republicans also face a tough calculation when deciding whether to support Mr. Trump. According to a veteran House member, Tom Cole of Oklahoma, some members in red-leaning districts in blue states are more inclined to view supporting Mr. Trump as helpful than those in heavily Hispanic districts.

Fine. They are most concerned about party unity Mitch McConnell Mitch McConnell, the Senate majority leader, ultimately wants to retain Republican control of the Senate in 2016 and protect those up for re-election in 2018. He said in a short statement, “I have committed to supporting the nominee chosen by Republican voters, and Donald Trump, the presumptive nominee, is now on the verge of clinching that nomination.” Several other Republicans have said they will “support the nominee” but have expressed concerns about some of his positions, like temporarily barring Muslims from entering the country.