Sen. Thom Tillis will be among those Republican senators to vote in favor of a resolution against President Donald Trump’s declaration of a national emergency at the border, the North Carolina Republican made public Monday, increasing the chances that the resolution will be sent to the White House.

Tillis, who is up for re-election in 2020, wrote in an op-ed for The Washington Post that while he favors border security, he is concerned the President has overreached with the national emergency declaration.

“As a U.S. senator, I cannot justify providing the executive with more ways to bypass Congress,” he wrote. “As a conservative, I cannot endorse a precedent that I know future left-wing presidents will exploit to advance radical policies that will erode economic and individual freedoms.”

Republicans control 53 seats in the chamber. If all Democrats vote for it, they will still need four Republican votes to help them stop Trump’s national emergency declaration. They have two, now that Tillis and Maine Sen. Susan Collins, who’s also up for re-election in 2020, have said they’ll join.

Other Republicans have also expressed concern about Trump’s decision to declare a national emergency as well.

Sen. Lisa Murkowski, a moderate Republican from Alaska, told a home-state TV station that she would “probably” support the proposal of disapproval.

“Not because I disagree with the President when it comes to border security, (or) certainly national security, but because I think it’s so important that there be clear lines when it comes to the separation of powers,” Murkowski told KTUU in Anchorage. “There’s going to be a great deal of debate as to whether or not the legal authority is there. I would suggest there probably is. The question is … is this over and above the authority that has been granted specifically to the Congress itself?”