WASHINGTON — President Trump has decided to roll out the big cannon.
A White House official said he will declare a national emergency to build a wall on the border with Mexico, using money from other federal accounts, after Congress declined to authorize sufficient funds to satisfy him in legislation that averts another government shutdown.
Mr. Trump will be wielding extraordinary power to get his way. Democrats strenuously dispute that there is a national security crisis on the border that warrants using the kind of presidential authority that in the past has been used for grave matters like the Sept. 11 terrorist attacks.
Here are six takeaways from Mr. Trump’s action.
Trump will go to almost any length to appease his base
Republicans in Congress, including Senator Mitch McConnell of Kentucky, the majority leader, were fine with the spending deal that they reached with Democrats to keep the government open.
But more hard-line elements within the party scalded Mr. Trump with criticism, including the Fox host Laura Ingraham and the conservative commentator Ann Coulter. But as The New York Times reported early Friday, the president felt cornered into accepting the deal and agreed to it only with Mr. McConnell’s promise to support an emergency declaration.
Still, the White House assuaged some other skeptics of the funding deal, namely Sean Hannity on Fox and the radio host Rush Limbaugh, both of whom in effect announced the president’s decision in advance and encouraged their followers to fall in line.
Mr. Trump is willing to risk the blowback, even from members of his party, and a possible court defeat, if it means he can tell his core supporters that he did all he could to build the wall.
Democrats probably can’t stop him, but they can make it awkward
Democrats cannot stop the president from issuing the declaration, but they can make it very uncomfortable for Republicans.
They can vote to terminate the president’s declaration on the grounds that there is no emergency — there is strong sentiment among Democrats to do that — which would force Republicans in the Senate to make a tough vote over Mr. Trump’s extraordinary exercise of power.
Already, Senator Susan Collins, Republican of Maine, has been sharply critical of the president using his authority this way, and fellow Republican Senators Marco Rubio of Florida and Rand Paul of Kentucky also have been highly skeptical. Mr. Paul called it “extraconstitutional.”
So the president’s action will force Republicans to decide whether to back him — and then set a precedent for a future Democratic president to use power this way — or embarrass Mr. Trump with a vote that could undo his declaration. The president could veto the resolution, and the declaration would likely remain in place because there would not be sufficient votes to override it, but his standing would be undermined.
Pulling money from elsewhere could make new enemies
Mr. Trump will have to find money from other federal programs to make up a $4 billion shortfall from his initial demand for border wall funding. He can do this by taking money from other military construction or from other funding for projects like disaster relief.
Each of those pots of money comes with a specific constituency that authorized it in the first place, and those constituencies may not be pleased to see it used for another purpose.
What about a court challenge?
If the president follows through with a declaration, a court challenge is a near certainty. A party opposing the president would probably seek an injunction — a halt in the action — while the matter was litigated. Yet every day that the wall was not built could undermine Mr. Trump’s fundamental premise that there is an emergency at the border.
The challenges are likely to be many, in jurisdictions from coast to coast, increasingly the chances that new construction would not start any time soon.
Watch how Nancy Pelosi responds
Speaker Nancy Pelosi has been among the few Democrats who seem to be able to stare down the president.
In this case, she has offered a not-so-subtle warning about what she sees as an abuse of the emergency authority. She pointed to the mass shootings in the United States, and noted that perhaps the president should issue a national emergency about guns.
That could be a mere preview of how she and the Democrats will frame the case against the president, starting with the idea that he has abused is constitutional authority.
Expect to hear a lot from Ms. Pelosi about a basic tenet of American government, that Congress is a coequal branch of government that is not cowed by presidential whim.
Trump handed his challengers an argument
Democratic presidential candidates already believe they have a list of reasons to deny Mr. Trump a second term. In turn, he has increasingly tried to cast them as far-left socialists.
The national emergency declaration may give Democrats an opening to turn his case upside-down, allowing them to argue that he has governed as an authoritarian who put his desires for a pet project above democracy.