Senate Majority Leader Mitch McConnell (R-Ky.) has privately cautioned President Donald Trump not to declare a national emergency to build his southern border wall, The Washington Post reported Friday. He warned Trump that such a declaration might split the GOP and that Congress could pass a resolution opposing it, two Republican sources familiar with the conversation told the newspaper.

In such a situation Trump might be forced into the first veto of his presidency — against his own party, McConnell pointed out, according to the sources.

The exchange reportedly occurred in a face-to-face meeting in the White House that involved only the two men.

It’s difficult to know if the president’s repeated threats to declare an emergency to take the legislature out of the picture to build the wall are just bluff or serious. Trump has insisted he will not agree to any deal unless it includes money for a wall. But Speaker Nancy Pelosi (D-Calif.) flatly told reporters Thursday: “There’s not going to be any wall money in the legislation.”

The temporary funding bill that re-opened parts of the government expires Feb. 15.

“We will be looking at a national emergency because I don’t think anything’s going to happen” concerning an agreement, Trump told reporters at the White House.

Some GOP legislators have already spoken out against an emergency declaration — and against another government shutdown. GOP Florida Sen. Marco Rubio said that an emergency declaration was a “terrible idea” and that he would oppose it. Sen. John Cornyn (R-Tex.) said last month that to “give the president authority basically to do that all by himself would, I think, stretch constitutional boundaries.”

McConnell has expressed support for some kind of negotiated agreement.

“I’m for whatever works, which means avoiding a shutdown and avoiding the president feeling he should declare a national emergency,” McConnell said in his weekly news conference in the Capitol.