Republicans have good reason to be deeply nervous. Here’s why: According to one of the country’s leading experts on national emergencies, it appears that House Speaker Nancy Pelosi (D-Calif.) can trigger a process that could require the GOP-controlled Senate to hold a vote on such a declaration by Trump — which would put Senate Republicans in a horrible political position.

Trump reiterated his threat to declare a national emergency in an interview with CBS News that aired over the weekend. “I don’t take anything off the table,” Trump said, adding in a typically mangled construction that he still retains the “alternative” of “national emergency.”

AD

AD

But Pelosi has recourse against such a declaration — and if she exercises it, Senate Republicans may have to vote on where they stand on it.

Trump does have the power to declare such an emergency under the post-Watergate National Emergencies Act, which also requires him to identify which other specific statute delegating emergency powers he’s invoking. Trump is expected to rely on one of several statutes that authorize military officials, in a presidentially declared emergency, to redirect funds for purposes that are either “essential to the national defense” or support “use of the armed forces.”

The Post reports that acting White House chief of staff Mick Mulvaney has privately told Trump that a national emergency is “viable,” and officials at the Army Corps of Engineers are searching for ways to build the wall. This would be challenged in the courts, which would have to decide whether the statute Trump invoked actually does authorize this type of spending.

AD

AD

But Pelosi has a much more immediate way to challenge Trump’s declaration. Under the National Emergencies Act, or NEA, both chambers of Congress can pass a resolution terminating any presidentially declared national emergency.

What Pelosi can do

Elizabeth Goitein, who has researched this topic extensively for the Brennan Center for Justice, tells me that if Pelosi exercises this option, it will ultimately require the Senate to vote on it in some form as well. The NEA stipulates that if one chamber (Pelosi’s House) passes such a resolution, which it easily could do, the other (McConnell’s Senate) must act on it within a very short time period — forcing GOP senators to choose whether to support it.

AD

Alternatively, Goitein notes, the Senate could vote not to consider that resolution or change its rules to avoid such a vote. But in those scenarios, the Senate would, in effect, be voting to greenlight Trump’s emergency declaration.

AD

The NEA lays out a timetable for this process, and by Goitein’s reading, it would all take place within the protracted period of barely longer than a month. “In short, there could be 36 days between introduction of the resolution in the House and a vote on the Senate floor,” Goitein told me, “but that vote would have to happen,” and once it did, one way or the other, it would put senators “on record.”

A Democratic leadership aide tells me the House might opt for this move if Trump takes the plunge. “The House will vigorously challenge any declaration that seeks an end run around Congress’s power of the purse,” the aide says.

AD

Why Republicans are panicking

Republicans themselves have let it be known that they fear this scenario. Sen. John Cornyn (R-Tex.), an adviser to McConnell, has said that a Senate vote on any Trump-declared national emergency would be inevitable, and McConnell has told Trump that Congress might have to act in such a fashion. Both of these appear to be references to a scenario like the one outlined above.

AD

Both men have also said this would deeply divide Republicans. One unnamed Republican senator even told the Washington Examiner that Trump would suffer major defections in such a vote.

GOP senators would have to decide between going on record in favor of a presidential declaration of a national emergency for something that everyone knows is based on false pretenses, a move that would be opposed by two-thirds of the country, or opposing it and possibly forcing a Trump veto (which they then would have to decide whether to override), enraging Trump’s base.

AD

Trump loves his pliable acting Cabinet members

Indeed, it’s worse than this. The Wall Street Journal reports that Trump is privately satisfied with his many “acting” Cabinet members — that is, ones who haven’t been confirmed by the Senate — because they are “more beholden to the Oval Office.” And under a national emergency, it would fall to Trump’s acting defense secretary Pat Shanahan to make the wall happen and perhaps to make a public case for what everyone knows is utter nonsense:

But as Julian Sanchez points out, avoiding this is exactly why we have the process of Senate confirmation. As Alexander Hamilton wrote, it is supposed to deter a president from filling important slots with people who possess a “pliancy” that will render them “obsequious instruments of his pleasure.”

AD

AD

That, of course, is exactly what Trump wants from his underlings. So we could be looking at a remarkable scenario: The acting defense secretary who would realize the wall — without authorization from Congress — won’t have been confirmed by the upper chamber, which may then end up declining to block Trump’s national emergency, neutering itself further.

And so, GOP senators are basically pleading with Trump not to force them into the position of choosing between that scenario and acting to terminate Trump’s emergency. Of course, the latter would make the shrinking Trump base very, very angry, which may be the most terrifying outcome of all.

Read more: