Joshua Roberts / Reuters

There was a climactic moment Thursday afternoon as Majority Leader Mitch McConnell announced on the Senate floor that President Donald Trump would sign a compromise deal on border-security funding, but would also declare a national emergency to try to build his wall. What happens next will be a test of the mettle of Republicans in the Senate—though if the past is any indication, it’s likely to be more of an anticlimax.

The announcement, confirmed by White House Press Secretary Sarah Sanders, capped a tense afternoon, as the mood on Capitol Hill shifted from an expectation that Trump would sign the deal to jitters that he might not. McConnell’s announcement ended one acute, Trump-created crisis—the threat of a second government shutdown, starting Friday—but the expected emergency declaration creates another. (Trump is slated to sign the bipartisan deal on Friday morning.)

Republicans have warned Trump against declaring a national emergency for weeks. Their concerns spring from both principle and pragmatism. Emergency declarations are a gray area of the law and raise concerns about executive power. It isn’t clear how an emergency declaration to build a border wall would work, nor whether courts would approve it in the inevitable legal challenge to come. Senator John Cornyn of Texas, a close ally of McConnell’s, has said he opposes the idea because it could empower a future Democratic president to proclaim an emergency of his or her own.

Following a declaration, the White House would still have to come up with funding for the wall without Congress’s help, which would require overriding appropriators’ spending decisions. That might well be unconstitutional and in any case risks infuriating appropriators, who jealously guard their power.

McConnell, as the head of the Senate and the top Republican on Capitol Hill, has been one of those warning against an emergency declaration, delivering his opinion in his typically understated, bland way. “I don’t think much of that idea,” McConnell told Charlie Homans of The New York Times Magazine in January. “I hope he doesn’t go down that path.”

He also reportedly warned Trump privately against the idea. McConnell told the president that if he declared an emergency, Congress might try to overrule him with a resolution, and that enough Republicans might join with Democrats that the resolution would succeed. Opinion among Republicans is not uniform; Senator Lindsey Graham of South Carolina has been a cheerleader for a declaration. But many Republicans have expressed misgivings, including on Thursday, and Trump’s decision to go forward sets up a test of their will to oppose the president.

Yet if McConnell himself is any indication, they are unlikely to push back. He flip-flopped on Thursday, announcing he’d support the president, despite his past public and private warnings against an emergency declaration. The GOP’s acquiescence wouldn’t be a surprise: While I have written that Trump almost always folds—and his decision to accept the compromise funding bill is yet another example—Republican members of Congress almost always fold, too.

With control of the one chamber, Democrats can force a battle over funding through spending bills, but only the GOP-controlled Senate can decide the fate of the emergency declaration by joining the House to vote against it. In one sign of their weak resolve, Republican members were reportedly demanding to know whether Trump would sign the funding bill before they held a vote—effectively delegating their decision to the White House.

That fits with the pattern. Despite having already passed a funding bill without money for the wall in December, they declined to force Trump’s hand and end the recent shutdown by voting for anything without his stamp of approval. Trump has stonewalled them on a report over the murder of the journalist Jamal Khashoggi, which the White House is legally required to provide, eliciting only some mildly affronted quotes from senators. They gave in to his decision to levy a range of tariffs on imports. Because of this pattern, it was especially surprising when the Senate voted to rebuke Trump’s plans to withdraw U.S. forces from Syria—in a nonbinding resolution.

The reasons for Republicans’ faintheartedness are varied. Some are worried that opposing him could generate career-ending primary challenges, a fear that is probably correct. In McConnell’s case, as Homans reported, the majority leader has apparently concluded that any Faustian bargain with Trump is worth the opportunity to remake the federal courts with conservative judges.

Now Senate Republicans have another chance to demonstrate their willingness to stand up to the president. The results could have far-reaching implications. Their actions will help determine the fate of the wall, an enormous undertaking that could cost $25 billion or more. They will also help determine whether Trump and future presidents are able to find ways to undertake huge, costly projects without congressional approval by using emergency declarations as an end run around legislators.

Each encounter between Trump and the Senate that ends in a senatorial surrender is also a signal to Trump about what could happen should he decide to fire Special Counsel Robert Mueller or take other unprecedented steps to protect himself from investigations. McConnell has refused to allow the Senate to vote on a bill defending Mueller, but he has also said he doesn’t think Trump is going to fire him. Former House Speaker Paul Ryan told Homans that he and McConnell had a contingency plan if he did. Then again, McConnell didn’t think Trump was going to declare a national emergency either.

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