The Republican Party was at the brink of civil war on Sunday as Donald Trump signaled he would retaliate against lawmakers who withdraw their support from his campaign, and senior party leaders privately acknowledged that they now feared losing control of both houses of Congress.

Even before Trump’s second debate against Hillary Clinton, the party faced an internal rift unseen in modern times. A wave of defections from Trump’s candidacy, prompted by the revelation of a recording that showed him bragging about sexual assault, was met with boastful defiance by the Republican presidential nominee.

On Twitter, Trump attacked the Republicans fleeing his campaign as “self-righteous hypocrites” and predicted their defeat at the ballot box. In a set of talking points sent to his supporters Sunday morning, Trump’s campaign urged them to attack turncoat Republicans as “more concerned with their political future than they are about the country.”

The pressure from Trump did not deter new expressions of resistance on Sunday: Gov. Bill Haslam of Tennessee, a former chairman of the Republican Governors Association, announced he would not vote for Trump. So did multiple members of Congress, including Rep. Kay Granger of Texas, the lone woman in the state’s large delegation.

Paralysis: But much of the party appeared to be in a state of paralysis, uncertain of how to achieve political distance from Trump without enraging millions of voters who remained loyal to his campaign.

Republican leaders in the House of Representatives offered scant guidance to their members, scheduling a conference call for Monday morning but leaving lawmakers to fend for themselves in the meantime, according to two members of Congress, who spoke on the condition of anonymity.

The Republican National Committee took on the aspect of a fortress: Numerous Republicans who sought to reach the committee’s top officials said they were unable to get through, though Reince Priebus, the committee’s chairman, flew beside Trump to the debate in St. Louis, even as Republican elected officials rejected their nominee en masse.

Stepping up: Facing a vacuum, several Republicans who have long opposed Trump have stepped forward to help shore up the party’s embattled majorities.

Mitt Romney, the party’s 2012 presidential nominee and a vocal critic of Trump, has laid out plans to campaign more publicly for Republican Senate candidates in the coming weeks, according to two people familiar with his plans, which were confirmed by an aide. Gov. John Kasich of Ohio, another Trump foe who has already hit the trail for congressional candidates, plans to campaign soon for Sen. John McCain in Arizona and for Joe Heck, the party’s Senate nominee in Nevada, according to John Weaver, Kasich’s top political adviser.

But with no overarching strategy yet in place for abandoning their nominee, Republicans beat a ragged and improvised retreat from Trump, pulling endorsements here and scolding him there, and preparing to flee more visibly in the event of another disastrous debate on Sunday night.

Steven Law, a longtime lieutenant of the Senate majority leader, Mitch McConnell, R-Ky., said the party had descended into chaos.

“The Republican Party is caught in a theater fire; people are just running to different exits as fast as they can,” said Law, who now heads the super PAC American Crossroads.

One member of the House Republican leadership, conceding its majority was now in jeopardy, compared the situation to the 2006 scandal involving a Florida congressman’s inappropriate conduct with congressional pages. If that scandal was the equivalent of a house fire, this lawmaker said, Trump had brought on the political equivalent of a nuclear attack.

Democrats: For Democrats, Trump’s rapid unraveling has opened a new universe of political opportunity. They are now confident that they will take control of the Senate, and the party plans this week to lay the groundwork for what could become a sweeping expansion of the political map.

With Trump sliding in the presidential race, senior Democratic officials had already been nudging Clinton to rearrange her campaign schedule and advertising in ways that could help lift Democrats in close congressional races. Now, top Clinton advisers said they would consider doing just that.

The campaign was planning to survey an array of Republican-leaning states this week, including Arizona, Georgia, Missouri and Indiana, to determine how competitive Clinton is with Trump, according to a senior Clinton adviser who spoke on the condition of anonymity.

Sending Clinton to those states may be of little assistance to the party’s candidates, but an infusion of money dedicated to voter turnout could ensure that she enters the White House with a solid Senate majority and help Democrats make substantial gains in the House.

Democratic strategists involved in House and Senate races said they envisioned Trump’s collapse precipitating a broad shift in the political landscape, with tossup races moving firmly into their hands, and campaigns that were once long shots suddenly becoming competitive. The Democratic Congressional Campaign Committee planned to do rapid polling early this week to measure the impact of Trump on the House battlefield.

Democrats said they had no intention of allowing Republicans to wash out the stain of associating with Trump: “Voters will see this for the craven act of self-preservation that it is, and it won’t save them,” said Meredith Kelly, a spokeswoman for the committee.

Loyalty: Barring an unforeseeable, if not miraculous, political recovery for Trump, the Republican exodus from his camp is expected to pick up pace in the coming days as lawmakers digest his debate performance and receive new polling on how voters are processing his apparent demise. Even then, Republicans may be hard-pressed to fully desert a nominee who maintains a powerful following in the party base.

That abiding loyalty is what alarms party strategists: Even if just 5 percent of the most reliable Republican voters do not vote or cast a ballot only for Trump, it would ensure that Republicans lose nearly every close congressional race.

Former Rep. Thomas M. Reynolds of New York, a former chairman of the National Republican Congressional Committee, said party polling had found voters tilting toward Democrats in congressional elections, even before the latest revelations about Trump. His setbacks threatened to push voters further away from Republicans, Reynolds said.

But Reynolds cautioned that lawmakers might be at risk of fatal backlash from Trump’s supporters if they oppose him in the final weeks of the race, leaving no easy option. Resentful Trump backers, Reynolds said, “could end up coming in and voting for Trump and stopping there.”

For Trump, too, there may be risks to attacking other Republicans. While most of his advisers expressed frustration and outrage at being deserted by the party over the weekend, at least some encouraged Trump to pull back from all-out war. One senior adviser to Trump conceded the acute need to bring Republican voters “back home” in the presidential race and said Trump’s outbursts at other Republicans could have the opposite effect.

Several party strategists said that for the time being, they had advised candidates chiefly to redouble their attacks on Democrats. Robert Blizzard, a Republican pollster, said that only by making Democrats “unacceptable” could Republicans offset the burden of carrying Trump.

“Endorse him or denounce him, it doesn’t change the fact that Democrats will attempt to tie our candidates to Trump at every opportunity,” Blizzard said. “What our campaigns can control is the ability to make Democratic candidates for U.S. Senate, Congress and other state and local offices unacceptable.”

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