Republicans woke up Columbus Day morning to the sights and sounds of the wheels coming off their midterm-election bus and their legislative jalopy. First came a widely publicized war of words between President Trump and the prominent Republican senator, Foreign Relations Committee Chairman Bob Corker. Then came a Bloomberg News story by Jennifer Jacobs and Bill Allison laying out Steve Bannon’s intention to back challengers to most of the GOP senators seeking re-election next year.

The Trump-Corker contretemps began last week when the Tennessee lawmaker, who had been a top contender to be Trump’s running mate as well as secretary of State, took an obvious shot at the president when he told reporters that Secretary of State Rex Tillerson, Secretary of Defense Jim Mattis, and White House Chief of Staff John F. Kelly “are those people that help separate our country from chaos.” Corker amplified his criticism on Fox News Sunday, charging that Trump was treating his office like “a reality show,” with reckless threats toward other countries that could set the nation “on the path to World War III.”

The tweet wars then began in earnest. Trump fired back that Corker “didn’t have the guts” to run for re-election, and Corker reponded by saying, “It’s a shame the White House has become an adult day care center. Someone obviously missed their shift this morning.” After adding that the former reality television star was “like he’s doing ‘The Apprentice’ or something,” Corker concluded that “he concerns me,” and it should “concern anyone who cares about our nation.”

In a New York Times interview later Sunday, this in a phone call with Jonathan Martin and Mark Landler, Corker said that “I know for a fact that every single day at the White House, it’s a situation of trying to contain him.” Trump fired up his twitter gatling gun and wrote that “Bob Corker gave us the Iran Deal, & that’s about it. We need HealthCare, we need Tax Cuts/Reform, we need people that can get the job done!”

While Trump has been highly critical of the Republican-led Congress in general, and the Senate Republican leadership in particular, for their failure to repeal and replace Obamacare, his exchange with Corker went to a darker place. Corker did what a lot of Republican leaders have been tempted to do — question the president’s maturity and stability, and speculate how that might affect his performance as commander-in-chief.

Over the last year Trump has singled out for criticism two endangered GOP incumbents up for re-election this year, Jeff Flake of Arizona and Dean Heller of Nevada. He also has engaged in an on-going feud with Senate Majority Leader Mitch McConnell. If Trump is to get anything done legislatively without having to depend on Senate Minority Leader Chuck Schumer and House Minority Leader Nancy Pelosi, he must have the support of Corker, McConnell, Flake, and Heller. The opportunities to align with Schumer and Pelosi are likely to be few and far between.

Citing three sources “familiar with his plans,” the Bloomberg News article reported that Bannon “plans to support as many as 15 Republican Senate candidates in 2018, including several challengers to incumbents. He’ll support only candidates who agree to two conditions: They will vote against McConnell as majority leader, and they will vote to end senators’ ability to block legislation by filibustering. Bloomberg went on to say that only Senator Ted Cruz of Texas is safe because he’s considered sufficiently conservative and seen to be moving toward the more populist approach Bannon favors.

Bannon has already scored a victory in Alabama by successfully backing former state Supreme Court Chief Justice Roy Moore against a Luther Strange, a senator appointed by the GOP establishment. The Bloomberg piece reported that Bannon was targeting incumbents Flake, Heller, Nebraska’s Deb Fischer, Wyoming’s John Barrasso, and Utah’s Orrin Hatch, and the New York Times reported on Sunday that another Bannon favorite, Erik Prince, founder of the controversial security firm Blackwater, was considering a challenge to Barrasso. In the event that Sen. John McCain leaves office early — he is undergoing treatment for a virulent form of brain cancer — Bannon has indicated a preference for Paul Gosar, a state representative and tea party activist. In the race to replace Corker, Bannon intends to support Rep. Marsha Blackburn.

Almost any conversation with congressional Republicans starts and ends with the need to cut taxes, now that tax reform no longer seems possible. Having failed to pass any legislation of real significance this year, and with a president who carries little weight on Capitol Hill, Republicans desperately need to put some points on the board. They are banking on passing a tax cut that’s meaningful, that voters can see, feel, and touch. If they pass something insufficiently large, the political payoff will be commensurately small.

With 25 Democratic Senate seats up next year, ten in states Trump carried, five in states the former real estate developer won by 19 points or more, this should be a year for the GOP to expand its current narrow 52-48 majority. Under different circumstances, the GOP could hope to boost their Senate numbers by four to seven seats, perhaps even reaching the magic 60-seat Senate super-majority level that could break filibusters on party line votes. But given their current disarray, Republicans will need to fight hard to gain any new seats, and losing one or two of their own seats would put their majority in jeopardy.

The stakes are even higher in the House where their majority status is in real danger. The party needs to sublimate its divisions, get mainstream Republicans to the polls, and persuade the Trump base to cast ballot for non-Trump Republicans. That’s a tall order. And it’s why last week’s news reduced the odds of the GOP retaining its majority from a good bet to even money.

More from the Cook Political Report