By Rebecca Davis O'Brien and Sadie Gurman 

Sixteen states on Monday filed a federal lawsuit challenging President Trump's national-emergency declaration to pay for a wall along the U.S.-Mexico border, setting up a showdown with the administration that could go to the Supreme Court and last through the 2020 election.

The complaint, filed in California's Northern District, seeks judicial intervention to stop the order and accuses Mr. Trump of "flagrant disregard for the separation of powers." The suit claims that the president's move undermined Congress by redirecting federal money -- some of which was intended for states -- toward the wall.

"President Trump has veered the country toward a constitutional crisis of his own making," the lawsuit said.

California led the lawsuit and was joined by Colorado, Connecticut, Delaware, Hawaii, Illinois, Maine, Maryland, Michigan, Minnesota, Nevada, New Jersey, New Mexico, New York, Oregon and Virginia -- all of which have Democratic attorneys general and all but one of which are led by Democratic governors.

Mr. Trump declared a national emergency Friday, after Congress passed a spending bill with $1.38 billion of funding for new wall construction, a fraction of what the president had sought. The move was designed to allow him to access billions of dollars from military-construction projects and other federal sources to build a wall on the border with Mexico. The declaration drew swift condemnation from Democrats and some Republicans in Congress.

The states seized in part on Mr. Trump's comment Friday that, "I could have done the wall over a longer period of time. I didn't need to do this" as proof that the declaration wasn't an emergency. The lawsuit says, "By the President's own admission, an emergency declaration is not necessary," adding that the federal government's data show there "is no national emergency at the southern border that warrants construction of a wall."

The Northern District of California, based in San Francisco, has ruled against the president before, particularly in cases involving the administration's immigration policies.

The White House didn't immediately comment on the suit.

House Democratic leaders are weighing a suit of their own, arguing Congress alone has the power to appropriate funds.

Public Citizen, an advocacy group representing Texas landowners whose property is threatened by the wall's construction, sued Mr. Trump on Friday, and groups such as the American Civil Liberties Union have also said they plan to do the same.

The lawsuits raise sweeping questions about the allocation of power among the branches of government, but any courtroom action will likely focus on more technical issues, said Peter Shane, a professor at the Ohio State University Moritz College of Law.

The states' lawsuit is likely to stall the implementation of the emergency declaration and generate protracted legal battles that could land before the conservative-dominated Supreme Court. The case may not be resolved before 2020, potentially making Mr. Trump's plan an issue in the next presidential election.

The legal attack is also likely to represent another roadblock for Mr. Trump in his efforts to follow through on his signature campaign promise of building the wall.

As in other legal challenges mounted by states against Trump administration measures, particularly on immigration, the states are expected to succeed in getting a judge to issue an injunction temporarily blocking Mr. Trump from accessing the $6.7 billion he is seeking to tap from the military and other sources, legal experts said. But it is unclear whether they ultimately will prevail, as courts have been reluctant to second-guess the president on national-security matters.

According to the lawsuit, the plaintiff states stand to lose millions in federal funding under the national emergency, including money supporting law enforcement and anti-drug efforts. The lawsuit also sites "irreparable environmental damage" that the construction of the wall would cause to California and New Mexico's southern borders and economic harm to states from the loss of military construction funding.

The states' best chance could be to argue that the border wall doesn't meet the statutory definition of a military construction project, as the president asserts, Harvard law professor Mark Tushnet said.

"It's not a slam dunk for them," he said, "But there's a decent chance they will ultimately prevail."

The Justice Department, as it has done in similar cases, will likely argue that the emergency declaration was based on national-security concerns, and the courts should give deference to the president in such decisions, legal experts said.

Mr. Trump indicated that he was prepared for a court fight. "We will possibly get a bad ruling. And then we'll get another bad ruling. And then we'll end up in the Supreme Court, and hopefully we'll get a fair shake," he said during his Friday announcement.

California Attorney General Xavier Becerra said Monday in a statement that Mr. Trump "admits that he will likely lose this case in court."

Mr. Trump's declaration followed two months of wrangling with lawmakers over the border wall, a dispute that precipitated a partial shutdown of the federal government.

In addition to Democrats, some Republican lawmakers have also been critical of Mr. Trump's declaration, saying the president's plan undermines Congress and sets a dangerous precedent if future Democratic presidents were to seek to declare emergencies over their priorities.

Democrats have said they are considering a joint resolution disapproving of the declaration once Congress returns from recess. While some Republicans have said they would vote against Mr. Trump, there likely aren't enough votes to overcome a presidential veto.

Previous presidents have signed dozens of emergency declarations, including those related to the Sept. 11, 2001, terrorist attacks and sanctions, but not for initiatives that Congress declined to fund.

Thousands of demonstrators in cities across the U.S. protested Mr. Trump's declaration on Monday, including outside the White House.

Mr. Trump, on Friday, said his action was critical to national security. "We're talking about an invasion of our country," he said.

Critics have also challenged Mr. Trump's assertion that border security is in crisis. The number of people apprehended at the U.S.-Mexico border -- seen as an indicator of illegal entries -- fell to the lowest total in 2017 in more than 40 years, though it then ticked up, according to U.S. Customs and Border Protection.

At the same time, the proportion of apprehensions involving children and families has surged.

California Gov. Gavin Newsom and Mr. Becerra had been threatening for days to file a lawsuit. The state's Democrat-dominated government has long been a legal foe of the Trump administration's, suing it over issues including the environment, immigration and internet regulation.

--Keiko Morris and Alejandro Lazo contributed to this article.

Write to Rebecca Davis O'Brien at Rebecca.OBrien@wsj.com and Sadie Gurman at sadie.gurman@wsj.com

(END) Dow Jones Newswires

February 18, 2019 21:42 ET (02:42 GMT)