With a Senate vote on nullifying Donald Trump’s border wall emergency declaration looming, Vice President Mike Pence is meeting privately with Republican senators to try and limit defections and embarrassment for the party and its president.

The vote is all but decided as four GOP senators have already said they’ll vote with Democrats to strike down the emergency declaration. The vote needs a simple 51-vote majority and there are 47 Democrats in the Senate.

A measure has already passed the Democrat-controlled House to nullify the declaration, though, Trump will exercise his veto powers and it will most likely end up for the courts to decide its legality.

Pence will reportedly meet with Sens. Thom Tillis (N.C.), Lamar Alexander (Tenn.) and Mike Lee (Utah), who are reportedly on the fence about whether to join the Democrats in rebuking the president’s authority.

The four GOP senators are Susan Collins of Maine, Lisa Murkowski of Alaska, Thom Tillis of North Carolina Rand Paul of Kentucky. Paul said he thinks the Supreme Court will ultimately strike the declaration down as unconstitutional because it takes power away from Congress, a co-equal branch of the U.S. government.

Per The Washington Post:

Those three senators have indicated varying levels of concern with the president’s emergency declaration, issued Feb. 15 to reroute billions of dollars for military construction projects toward Trump’s border wall instead. Tillis, who is up for reelection next year, has already stated his outright opposition on constitutional grounds and is one of four Republican senators who plan to vote in support of a disapproval resolution of the declaration. The vote is expected Thursday.

Alexander gave a lengthy, blistering floor speech urging Trump to use alternative methods of securing the money for the border wall but has steadfastly declined to say how he would vote on the disapproval resolution. And Lee is privately crafting legislation meant to return to Congress some of the emergency powers afforded to the president.

Many Senate Republicans have started to align behind Lee’s proposal, which would amend the National Emergencies Act of 1976 to say an emergency declaration would automatically expire after 30 days unless both chambers of Congress vote to approve it.

But the White House, in private, has been skeptical of the effort so far and is proposing some changes to it, according one of the people familiar with the discussions. One possible way to amend it more to the White House’s liking is to make that 30-day period in Lee’s proposal longer.