Earlier Wednesday, in another blow to Lee's efforts, House Speaker Nancy Pelosi, D-Calif., said that her chamber would not consider Senate legislation to rein in presidential powers, characterizing it as an attempt to give Trump "a pass" on violating the Constitution.
Later Wednesday afternoon, the Senate voted 54-46 - with seven Republicans joining all Democrats - to pass the resolution curtailing United States military support for a Saudi-led war in Yemen.
U.S. President Donald Trump participates in a briefing on "drug trafficking on the southern border" in the Roosevelt Room at the White House in Washington, U.S., March 13, 2019. Lee's bill addresses that concern by ending future emergency declarations after 30 days unless Congress votes to extend them. The official was not authorized to publicly discuss private conversations and spoke on condition of anonymity.
At stake is billions of dollars in funding for a wall along the U.S. -Mexico border that Trump is demanding but Congress has refused to fully provide.
Republicans control the Senate 53-47, meaning that four GOP defections would be enough to send the resolution blocking Trump's border emergency to the White House. But it could force Trump to issue the first veto of his presidency - and could mark a rare occasion where a significant number of Senate Republicans are willing to go on record to vote against Trump.
The author of the bill that would affect future emergency declarations, Utah Republican Mike Lee, said it would take back legislative powers that Congress gave away when it passed the National Emergencies Act of 1976.
The disapproval resolution passed the House with a vote of 245-182 with the help of 13 Republicans.
Vice President Mike Pence met with Republican senators this week to push Lee's plan, saying Trump would support it. Lisa Murkowski of Alaska, Susan Collins of ME and Rand Paul of Kentucky have all publicly announced their support for the resolution of disapproval, with more Republicans privately wrestling with their votes. Tillis and Collins face potentially competitive re-election fights in 2020.
The White House has been trying to avert defeat.
"If they really want to take a stand, they'll vote for the resolution tomorrow and then they'll override the president's veto", said Brown. And Republicans will not be able to vote to limit national emergencies later, to give themselves political protection from Thursday's vote.
Brown said he doesn't object to finding a "long term answer", to keep presidents from declaring emergencies in non-emergency situations, but said he didn't know of any cases where past presidents abused the law. Congress can vote to block a declaration, but the two-thirds majorities required to overcome presidential vetoes make it hard for lawmakers to prevail. "Let's tell the president he cannot use his overreaching power to declare an emergency when he couldn't get Congress to do what he wanted". On Tuesday, the Utah senator introduced a new bill that would leave Trump's current emergency declaration intact, while placing restrictions on the future exercise of emergency powers.