House Democrats will move quickly to challenge U.S. President Donald Trump’s declaration of a national emergency at the U.S.-Mexico border in order to shift billions of dollars from defense to construction of a southern border wall.

House Speaker Nancy Pelosi of California told reporters lawmakers would vote Tuesday on a resolution that Rep. Joaquin Castro, D-Texas, filed Friday that would attempt to reverse the president’s move. As of Friday morning, Castro said at least 226 House members had pledged to support the bill. One Republican congressman, Rep. Justin Amash of Michigan, has also signed on.

Blocking Trump's Emergency Declaration Won't Be Easy

Trump told reporters Friday that he "100 percent would veto" the measure if it passed both chambers of Congress. He added, though, that he did not think the resolution would pass because "we have too many smart people who want border security."

Blocking Trump's Emergency Declaration Won't Be Easy

The ranking member of the House Judiciary Committee, Rep. Doug Collins of Georgia, said in a statement, "House Democrats' angst over Congress' power of the purse is unwarranted, especially since the commander-in-chief's authority to redirect military funds for a national emergency is affirmed in a law."

Blocking Trump's Emergency Declaration Won't Be Easy

A declaration of a national emergency gives a president the power to temporarily address an urgent situation that Congress may not have time to immediately react to.

The U.S. Constitution does not specifically address the issue of a president declaring a national emergency. The 1976 National Emergencies Act, however, grants a president the authority to make that move with limitations that prevent the emergency from continuing indefinitely. Congress has given the president that power 58 times since 1979, including 31 declared national emergencies that are still in effect. The others were eliminated through congressional action.

Previous have been declared for natural disasters such as floods and hurricanes or in the case of the Sept. 11, 2011, terrorist attacks.

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It’s all a matter of money and of power. The Constitution gives Congress “the power of the purse,” a phrase lawmakers often repeat to emphasize their crucial role in setting the budget for the United States and then specifying how money should be spent through appropriations legislation.

In the current controversy, Congress was willing to provide just $1.37 billion in new funds for Trump’s proposed wall construction, while the president demanded nearly $6 billion. At that point, Trump declared an emergency.

Congressional oversight also prevents a president from unilaterally seizing power. National emergency declarations have no set definition or limits, making the move open to abuse. Past presidents have used emergencies to declare war and — in the case of President Franklin Roosevelt in 1942 — to intern thousands of Japanese-Americans during World War II.

Under that 1976 act, once the president acts, the Congress is supposed to meet to decide whether to continue the emergency or to terminate it. Lawmakers can vote at any time to terminate the emergency, requiring majorities of the House and the Senate.

If the House Democratic resolution introduced Friday passes both chambers of Congress and survives a veto, the president would not be able to move money already earmarked for Department of Defense projects to fund construction of sections of a wall at the U.S.-Mexico border. But Congress has never blocked presidential action this way before.

Trump for months has argued that he needs more than 300 additional kilometers (200 miles) of wall along the border to stanch the flow of illegal immigrants and drugs and halt human trafficking across the border.

Democrats disagree with that assessment. They argue that appropriators — the members of Congress who decide how federal money is spent — reached an agreement on border security spending that the president then signed into law, ending the threat of another government shutdown on Feb. 15.

They point to declining numbers of illegal immigrants crossing the U.S.-Mexico border as well as the president’s failure to act legislatively when the Republican Party controlled both chambers of Congress for the first two years of his presidency.

Additionally, the president undercut his own case when he seemingly acknowledged that the “emergency” was not urgent.

“I didn’t need to do this," Trump said in his Rose Garden press conference announcing the move. “I just want to do it faster.”