President Donald Trump is stuck between a wall and his constitutional limits.

His attempt to use a government shutdown to force Democrats into passing funds for a border wall, the quintessential promise of his 2016 campaign, failed miserably. Because of his own vicious rhetoric, he’s given Democrats no possible reason to concede to letting him build a single inch of the wall. So he’s reopened the government, supposedly in hopes that negotiations over border security will lead to some kind of mutually satisfactory agreement, even though nobody really thinks that it will. That leaves Trump with one more card to play: Declare a national emergency and use his presidential authority to order the wall built.

There are only two real problems with this strategy: Many legal and constitutional experts think it’s a gross violation of his authority, and it could tear the Republican Party apart.

Sen. Lindsey Graham (R-SC), on the one hand, is urging the president to go forward with this plan. Graham, who was once a fierce critic of Trump, has now become his lackey, and he has concluded that building a wall by whatever means necessary is key to the survival of the president and the GOP.

“This is about more than a barrier,” Graham said at a speech in Greenville, South Carolina, according to Bloomberg. “This is about us as a 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,” he declared. “This is the defining moment of his presidency. It’s not just about a wall, it’s about him being treated different than every other president.”

He also sounded a note of warning for the GOP if Trump tries to do it on his own: “But there could be a war within the Republican Party over the wall.”

The Washington Post reported over the weekend that Senate Majority Leader Mitch McConnell cautioned Trump against the national emergency declaration:

At least a half-dozen Republican senators are fiercely opposed to the idea of an emergency declaration, generating enough opposition that a disapproval resolution could pass the Senate with the support of the 47 Democrats and a handful of GOP senators — the scenario about which McConnell warned Trump. Republicans expect that Trump would veto the resolution, and that the House and Senate would not be likely to muster the supermajority vote needed to override his veto.

A disapproval resolution on a presidential emergency declaration is rare, so exactly how the process would play out is uncertain. But it could expose new rifts within the GOP on Trump’s signature issue of a border wall, creating a portrait of disunity that most Republicans would like to avoid.

An emergency declaration would also risk further political damage to Trump, whose disapproval rating rose significantly over the 35-day partial government shutdown as more Americans faulted the president than Democrats for the standoff.

And CNN reported Monday that many GOP lawmakers are going public with their objections to the idea.

“There are a lot of reservations in the conference about that and I hope they don’t go down that path,” said Senate Majority Whip John Thune (R-SD).

“The whole idea that presidents — whether it’s President Trump, President Warren or President Sanders — can declare an emergency and somehow usurp the separation of powers and get into the business of appropriating money for specific projects without Congress being involved, is a serious constitutional question,” said Sen. John Cornyn (R-TX).

Writing for the Take Care blog,  Constitutional Accountability Center’s Chief Counsel Brianne Gorod explained why Trump’s use of the emergency powers should be considered illegitimate:

Against the background of the concerns that animated the passage of the National Emergencies Act, there seems to be little basis to think that the absence of specificity in these statutes means that the President is authorized to declare a national emergency on a whim.  Instead, it makes sense to try to give the words their ordinary meaning.  In common parlance, an “emergency” is “an unforeseen combination of circumstances or the resulting state that calls for immediate action” or “an urgent need for assistance or relief.”

There may be cases in which it is a close call whether a “national emergency” exists, but this isn’t one.  Indeed, at a Senate briefing earlier this week, “none of the [nation’s top intelligence] officials said there is a security crisis at the U.S.-Mexico border.”  That officials in the President’s own Administration don’t think there’s an emergency surely undercuts any claim that there is.

And the President himself has said that whether he declares a national emergency will depend on whether he can “make a deal with people that are unreasonable.”  That makes it sound like even the President doesn’t think there’s an urgent crisis at the border.

Despite their hypocrisy in many other situations, key leaders in the GOP still believe these considerations are important even when a Republican is in charge. So if Trump decides to tear the Band-Aid off and attempt to build a wall on his own, he could be spurned by the Senate Republicans that currently protect him. But if he doesn’t, he’ll likely face the wrath of his base.