California's Democratic Attorney General Xavier Becerra said Sunday that he will "definitely and imminently" file a lawsuit against the Trump administration to contest the declaration of a national emergency at the southern border.

President Donald Trump declared the emergency on Friday after signing a funding bill that included less than a quarter of the money he had requested for the construction of a border barrier, which he says is necessary to stop illegal immigration.

But Democrats like Becerra do not believe conditions at the border constitute an emergency.

"It’s clear that this isn’t an emergency – it’s clear that in the mind of Donald Trump he needs to do something to try to fulfill a campaign promise," Becerra said in an interview on ABC's "This Week." The construction of a border wall has been a central issue for Trump since he first announced he was running for president in 2015.

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"That doesn’t constitute a national emergency that would require us to essentially stand down on all sorts of federal laws and also violate the U.S. Constitution," said Becerra, a former congressman.

On Friday, Trump said the emergency declaration and a border wall was needed to combat what he characterized as an "invasion" of migrants across the southern border. He said open areas on the border allowed the free flow of drugs and dangerous criminals into the U.S.

By declaring a national emergency, along with other measures and the $1.375 billion Congress did approve, Trump will have about $8 billion to spend on border barrier construction – far more than the $5.7 billion he initially demanded.

White House adviser Stephen Miller, who is considered one of the chief architects of Trump's immigration policies, pushed back at the idea that the president's action was unconstitutional in an interview Sunday.

"Congress in 1976 passed the National Emergency Act and gave the president the authority, as a result of that, to invoke a national emergency in many different circumstances, but among them the use of military construction funds," Miller said on "Fox News Sunday."

Host Chris Wallace pressed Miller to cite another example from the 59 times presidents used the National Emergency Act where it was invoked to obtain money that Congress had refused to appropriate. Miller did not cite such a precedent and took issue with the premise of the question.

"They didn’t refuse to appropriate it," Miller said. "They passed a law specifically saying the president could have this authority. It’s in the plain statute. That’s the decision that Congress made, and if people don’t like that, they can address it."

Opponents of Trump's wall point to government statistics that the number of migrants crossing the border annually has declined in recent years. Many of the migrants who are making the journey are asylum seekers who seek out immigration officials when they arrive at the border.

They also point to government data that show that immigrants commit crimes at a lower frequency than U.S. citizens and that a wall is unnecessary because most of the drugs and people enter the U.S. at established points of entry. On Friday, Trump said he did not find that data credible.

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Critics who say the president is using his emergency powers to skirt Congress' constitutional authority over spending have pointed to his own word when he announced he would declare the emergency.

"I didn’t need to do this. But I’d rather do it much faster," Trump said at one point during the lengthy news conference on the White House lawn Friday.

"It’s become clear that this is not an emergency, not only because no one believes it is, but because Donald Trump himself has said it’s not," Becerra said. "Typically, our presidents have focused on issues where the national interests are clearly at stake. The national interests aren’t at stake here."

At least two lawsuits already have been filed in response to Trump's emergency declaration. The liberal watchdog group Public Citizen filed a federal lawsuit Friday in Washington, D.C., just hours after Trump's announcement. The group argues Trump exceeded his authority and disregarded the separation of powers outlined by the Constitution. The suit includes three Texas landowners whose property would be seized by the government through eminent domain to build part of the border barrier.

A second lawsuit was filed by the watchdog group Citizens for Responsibility and Ethics. It argues that the White House did not provide the supporting documents needed to justify the national emergency declaration.

Congressional Democrats vowed to do what they can to stop Trump from using his executive authority to shift the Defense Department money toward wall construction.

"The Congress will defend our constitutional authorities in the Congress, in the courts, and in the public, using every remedy available," House Speaker Nancy Pelosi, D-Calif., and Senate Minority Charles Schumer, D-N.Y., said in a joint statement Friday.

Rep. Joaquin Castro, D-Texas, said that he plans to introduce a "resolution to terminate" that could block the emergency declaration. Such a measure would likely pass in the Democrat-controlled House and could make it through the Senate, where a number of Republicans have objected to the precedent set by Trump's use of executive authority.

But if the resolution made it through both chambers, the president would almost certainly veto it. It is unlikely that enough congressional Republicans would join Democrats to override a veto.

"Obviously, the president is going to protect his national emergency declaration," Miller said Sunday when asked if he thought Trump would veto such a resolution.

Contributing: Alan Gomez and Christal Hayes

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