President Donald Trump has spent more than a week now teasing a possible emergency declaration at the southern border to get his wall built, a controversial, possibly unconstitutional move that would trigger immediate challenges from Democrats. His administration reportedly spent last week finalizing the strategy, and Trump hinted to reporters that he could announce the nuclear option in Tuesday evening’s State of the Union address, which he’s prepared with the help of anti-immigration ghoul Stephen Miller. (“I’m saying listen closely to the State of the Union,” he said. “I think you’ll find it very exciting.”) But it’s not just Democrats who have mobilized against Trump’s plan B—in recent days, the president has faced a groundswell of opposition to the plan from within his own party, with Republicans warning that an emergency declaration would be an abuse of power that could set a “dangerous precedent” moving forward.

“I hope he doesn’t do it,” Senator Roy Blunt of Missouri told Politico, echoing “a dozen G.O.P. senators” who alluded to a “broad effort” to dissuade Trump from going through with an emergency declaration. “We don’t think that’s necessary,” added Senator John Thune, the party whip. “There are concerns, and our members are conveying those.”

The opposition highlights fears within the G.O.P. about the legality of the move, and underscores the precarious position Trump has put himself and his fellow Republicans in as he’s escalated his fight for border-wall funding. In December, he said in a heated, televised meeting with Nancy Pelosi and Chuck Schumer that he’d be “proud” to shut down the government over the border wall—and then did just that. But it quickly became apparent that he’d overestimated his hand, and underestimated Pelosi, who outmaneuvered him at every turn, eventually forcing him to reopen the government without a penny of wall funding.

A bipartisan panel of 17 lawmakers now has until February 15 to come up with a border-security agreement that satisfies all parties involved, an ambitious undertaking on its face, but one that’s come to seem downright implausible as the president undermines the committee with threats to either shut down the government again, or bypass Congress with the nuclear option. But many Republicans, still reeling from the last impasse, would prefer a compromise over drastic action by Trump. Another shutdown would further hurt them politically, and an emergency declaration could be ruled unconstitutional. “The president’s going to get sued and it won’t succeed in accomplishing his goal,” Senator John Cornyn told Politico. “It strikes me as not a great strategy.”

With G.O.P. opposition building, it seems unlikely that Trump will make his emergency declaration at Tuesday’s address to Congress. But that will provide only temporary relief for Republicans. The deadline, after all, isn’t for another week, and failing a consensus, Trump could still put his plan B into action, fracturing the Republican Party. “To every Republican, if you don’t stand behind this president, we’re not going to stand behind you when it comes to the wall,” Senator Lindsey Graham, one of Trump’s closest allies, said during an event on Monday, adding that if the G.O.P. didn’t support the president wholeheartedly, he feared “a war within the Republican Party.”

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