Speaker Nancy Pelosi, D-Calif., and Senate Minority Leader Charles Schumer, D-N.Y., conduct a news conference in the Capitol about a continuing resolution to re-open the government on Friday, January 25, 2019.

The party signaled a protracted fight — both on Capitol Hill and in the court system — to challenge the president's executive action. The move would allow Trump to circumvent lawmakers to redirect government funds to build his proposed border wall, after a bipartisan spending bill gave him only about a quarter of the $5.7 billion he sought to construct barriers.

In a joint statement, House Speaker Nancy Pelosi, D-Calif., and Senate Minority Leader Chuck Schumer, D-N.Y., said lawmakers "will defend our constitutional authorities in the Congress, in the Courts, and in the public, using every remedy available." They added that the issue "transcends partisan politics" and pushed Republicans to "join us to defend the Constitution."

"The President is not above the law. The Congress cannot let the President shred the Constitution," the Democratic leaders said.

Even before Trump declared the national emergency, he sparked concerns about overreach of executive authority. Critics argue he has manufactured a crisis at the southern border to divert funding and fulfill a campaign promise, stepping on congressional authority in the process.

Some Republicans worried the action would create a dangerous precedent for future presidents, who would see a lower threshold for declaring an emergency over separate issues. In all, the president's move will likely trigger legal and legislative battles that will test GOP allegiance to Trump and the party's congressional leaders. Many Republicans who slammed what they called Obama administration overreaches wholeheartedly backed Trump's action Friday.

Both Senate Majority Leader Mitch McConnell, R-Ky., and House Minority Leader Kevin McCarthy, R-Calif., will not try to block Trump's executive action. In a statement Friday, McConnell appeared to blame Democrats for forcing Trump's hand by denying him the money he demanded for the wall. The border security deal came out of a conference committee with lawmakers from both parties and chambers.

"President Trump's decision to announce emergency action is the predictable and understandable consequence of Democrats' decision to put partisan obstruction ahead of the national interest," he said.

On Thursday, McCarthy said "we face a humanitarian and national security crisis at the border that must be addressed."

Other Trump allies, from Sen. Lindsey Graham, R-S.C., to Rep. Jim Jordan, R-Ohio, cheered the emergency declaration on Friday. But not all of the party's lawmakers agreed.

Sen. Rand Paul, R-Ky., said, "Extraconstitutional executive actions are wrong, no matter which party does them." In a statement Friday, Sen. Thom Tillis, R-N.C., "I don't believe a national emergency declaration is the solution" for border security.

Sen. Marco Rubio, R-Fla., said Thursday that he was "skeptical" whether he could back the president's move. Others — including Sen. Chuck Grassley, R-Iowa, and Sen. John Cornyn, R-Texas — have warned against declaring an emergency in recent weeks.

Still, criticizing the declaration and actually voting to block it are two different matters. Many Republicans may hesitate to rebuke the president.

Democratic House members have already pushed to introduce a resolution to disapprove of the president's action. While Pelosi and Schumer did not directly reference such a measure in their statement, it is one concrete way for Congress to challenge the president's declaration. They have to vote on it within 15 days.

If the Democratic-held House passes such a measure, the GOP-controlled Senate would have to take it up by law, putting pressure on Republican senators. Trump could also veto it, which would require a two-thirds majority in both chambers to overcome. With McConnell supporting the emergency declaration and Republicans holding 53 of 100 Senate seats, it is unclear whether lawmakers could block it.

Rep. Mark Meadows, a North Carolina Republican and another Trump confidant, argued Congress would lack the votes to override the president's veto.

"Given Congress will try to block this executive action, I'm seeing speculation Congress could override a POTUS veto w/ GOP votes. They will not. The votes will not be there," he tweeted.

Trump seemed prepared for a long fight Friday. "I expect to be sued" over the declaration, he said.

He argued that he had the authority to take the step, and thinks he will ultimately prevail in the Supreme Court. "I think we will be very successful in court," he said.

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