WASHINGTON — When Donald Trump goes low, congressional Republicans go quiet.
Their tolerance of Trump, even at the risk of humiliation, stems from a complex brew of political, policy and personal calculations that differ somewhat between party leaders and officials up for re-election.
But on one point, all sides agree: They have never seen a comparable situation, with a presidential nominee in open warfare with party leaders after a nominating convention. And Trump's provocations are making the Republicans' control of the Senate, perhaps even the House, more tenuous.
Many Republicans, even those whose contempt for Trump matches their ill will for President Barack Obama, still view the choice between Trump and Hillary Clinton as a binary one, with long-term implications for every policy area they care about, from judicial appointments to the economy to immigration. They believe that Trump, guided by a Republican-controlled Congress, will break their way more than Clinton ever would.
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For others, the vacancy on the Supreme Court — and its potential to reshape the high court's rulings for years — overshadows almost everything else, even their nominee's increasingly erratic statements and grasp of basic facts.
"The Supreme Court is probably the choice that will have the single most long-term effect on the nation," said U.S. Rep. Jason Chaffetz, R-Utah, where Trump is struggling to win over an overwhelmingly Republican state.
Congressional Republicans who are up for re-election — especially the handful like Sens. John McCain of Arizona and Kelly Ayotte of New Hampshire who still face primaries — have made a basic calculation. They have criticized Trump, but not withdrawn their endorsements. And party leaders have similarly decided that the more distance they put between themselves and Trump, the more likely they are to lose their congressional majorities.
Alienating Trump's supporters would cost them just enough votes to lose their seats. Their fears at this point appear justified. A recent poll conducted the last week of July by CBS News found that support for Trump among Republican voters rose to 81 percent from 79 percent.
So the leaders largely responded to Trump's attacks with feigned indifference.
"Republican elected officials are in a tough spot," said Nathan L. Gonzales, editor of The Rothenberg & Gonzales Political Report, a nonpartisan newsletter. "They are criticized for not listening to the grass roots and criticized for not denouncing the nominee chosen by the grass roots. Some Republicans are reluctant to attack Donald Trump because they'd risk alienating 35 to 40 percent of the party who supported him in the primaries."
Trump on Tuesday pointedly declined to endorse House Speaker Paul D. Ryan, the nation's highest ranking elected Republican, and verged on outright opposition to McCain and Ayotte, just hours after Obama challenged Republicans to denounce their nominee.
Both Obama and Trump have put Republicans into an untenable position: Criticizing their nominee could be seen as taking the advice of a president whom their core voters strongly dislike, potentially alienating the very people they need for re-election — but sitting idly as Trump attacks them and makes inflammatory comments may alienate more moderate voters.
"If you are repeatedly having to say, in very strong terms, that what he has said is unacceptable, why are you still endorsing him?" Obama asked during a news conference Tuesday.
Ryan's spokesman tersely responded that the speaker had never sought Trump's endorsement, and Ayotte more or less brushed off the matter, saying, "I call it like I see it," in reference to her defense of a fallen Army captain whose family Trump had derided. While many Republicans are hoping for ticket splitters — those who might vote Democrat for president but Republican down the rest of the ticket — the parsing is all the more difficult.
Many experts are skeptical that the approach can work. "In 2008 and 2010, voters did not draw distinctions," said Fergus Cullen, a former chairman of the New Hampshire Republican Party. "It was not like Passover, where the door was marked, 'This one should be spared.' No, the Angel of Death came in and said no 'Let's kill them all.'"
It is not just a question of individual desires to win re-election — although that certainly drives many of the statements about Trump that come short of rescinding an endorsement. Republicans believe they need to maintain the House and the Senate, through a hoped-for blend of votes from their base and anti-Trump split tickets, to pursue a policy agenda.
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"The speaker's goal, one that you set collectively with members of your conference, is to promote ideas and enact policies that make a difference," said Kevin Madden, a Republican operative who once worked for former House Speaker John A. Boehner. "The political reality, though, is that this goal can only be reached if members are not put at risk because the top of the national ticket underperforms."
Republican leaders also know that in an anti-Washington election cycle, the core of the party would likely be disposed to reject candidates who embody the Washington establishment.
This was the lesson that Sen. Ted Cruz of Texas learned when he was booed from the stage at the Republican National Convention last month for declining to get behind Trump, and accounts for some of the heat that Sen. Ben Sasse of Nebraska, a founder of the Never Trump movement, has taken from his party back home this year.
Then, there is the vehement opposition to Clinton, especially how they view her role in the Benghazi attacks, that has dominated the airwaves for years among Republicans.
"I happen to think that lying to the American people is a step way above and beyond some of the disappointing rhetoric of Donald Trump," said Chaffetz, chairman of House Oversight Committee. He added: " Nothing united Republicans more than Hillary Clinton."
Some still may pull away. On Tuesday, U.S. Rep. Richard Hanna, R-N.Y., said he would endorse Clinton for president, calling Trump "unfit to serve."
But Hanna is not representative of the broader Republican conference. "He came to Congress as an outsider and never fit neatly into the typical boxes," Gonzales said. "He's one of the most liberal members of the Republican conference. He would have had another serious primary challenge this year, if he had decided to seek re-election. But since he's retiring, he apparently feels even more freedom to say what's on his mind."
But if Trump falls in the polls and Republicans running for re-election start to realize they would do better separating from him and digging deeper for ticket-splitting voters, Hanna may not be alone.