Senate Majority Leader Mitch McConnell acknowledged Monday that he’s done the math, and he’s going to lose: The Senate will vote to terminate President Donald Trump’s national emergency on the Southern border. McConnell’s acknowledgment came after his fellow Kentuckian Sen. Rand Paul announced over the weekend that he would provide the 51st vote needed to block the president’s legally dubious maneuver. The final tally will likely run higher.

“I think what is clear in the Senate,” McConnell told reporters in Kentucky, “is that there will be enough votes to pass the resolution of disapproval, which will then be vetoed by the president and then in all likelihood the veto will be upheld in the House.” He’s correct on all counts. The White House has already issued an official veto threat, and the House didn’t come anywhere close to a veto-proof majority when it passed the resolution last week.

Even if Congress ultimately proves unable to block Trump, it won’t feel like a success for McConnell. The process he’s experiencing right now, in which Senate Republicans have to choose between their principles and their president under a bright spotlight that could otherwise be focused on more valuable political terrain, is exactly why he didn’t want the president to declare the national emergency in the first place.

As a morally flexible legislative leader, McConnell thinks less in terms of right versus wrong than unifying versus divisive. McConnell might say that he, personally, is a little uneasy about the president stealing money from elsewhere to build a wall. But what makes him truly uneasy is that he knows some members of his caucus feel quite strongly about protecting Congress’ constitutional power of the purse, or quite strongly about winning re-election in a purple state in 2020.

When a Republican is reading the Federalist Papers to explain her problem with what other Republicans are doing, McConnell’s agenda has been derailed.

That’s why, when McConnell was advising Trump earlier this year not to declare a national emergency, his main argument wasn’t that it would violate Mitch McConnell’s Sacred Constitutional Principles or provide the next Democratic president a new avenue for addressing climate change. It was that it would be a divisive issue within his caucus, and that divisiveness would be well-documented.

“Senate Majority Leader Mitch McConnell cautioned President Trump privately this week about the consequences of declaring a national emergency to build his border wall,” the Washington Post reported on Feb. 1, “telling him the move could trigger political blowback and divide the GOP.” And he was right.

The Senate Republicans who have already come out against the national emergency have not done so quietly. Paul, who announced his decision in a Fox News editorial, wrote that he “would literally lose my political soul if I decided to treat President Trump different than President Obama,” and that “the only way to be an honest officeholder is to stand up for the same principles no matter who is in power.” If you’re Mitch McConnell reading this, all you’re seeing is one of your senators calling most of your other senators dishonest officeholders.

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North Carolina Sen. Thom Tillis, who is moving toward the center ahead of his re-election campaign, similarly wrote that he was just standing by the same principles against executive overreach that he stood by under Obama. Maine Sen. Susan Collins, who joined with Democrats to introduce the Senate version of the disapproval resolution, cited James Madison in the Federalist Papers to justify this position. When a Republican is reading James Madison in the Federalist Papers to explain her problem with what other Republicans are doing, Mitch McConnell’s agenda has been derailed.

In the coming days, McConnell will watch as other critical members of the Republican Senate majority choose to split the baby. Does Colorado Sen. Cory Gardner make the sensible general-election decision in his lean-blue state, even if it invites the wrath of the president? Does Texas Sen. Ted Cruz follow Rand Paul, or does he deliver the punchline to his years of lecturing speeches about the Constitution? Does Florida Sen. Marco Rubio, previously a vocal opponent of the national emergency, add another entry to his list of caves?

These are the sorts of no-win decisions that McConnell hoped to protect his conference from. In a world where Trump opted not to pursue the national emergency, the poor politics of a debate over “the wall” would finally be in the rearview. McConnell would be using floor time to cleave Democrats, rather than the other way around, by forcing them to vote repeatedly on “banning cows” or ending employer-sponsored health insurance.

This might have been the happier, alternate dimension McConnell saw dissipate before his eyes when, on Feb. 14, he announced on the Senate floor that the president would declare a national emergency, and that he had agreed to support it.