US President Donald Trump has demanded funding for his long-promised US-Mexico border wall to halt “a growing humanitarian and security crisis”.
But in his first TV address to the nation from the Oval Office, Mr Trump did not declare a national emergency to bypass Congress and build the barrier.
In a televised rebuttal, Democratic leaders accused the president of holding the American people hostage.
Both sides are trying to gain an edge amid an 18-day government shutdown.
In an eight-minute address on Tuesday night carried live by all the major US television networks, Mr Trump said: “This is a humanitarian crisis, a crisis of the heart and a crisis of the soul.”
He added: “The federal government remains shut down for one reason and one reason only: because Democrats will not fund border security.”
The Republican president wants $5.7bn (£4.5bn) to build a steel barrier, which would deliver on his signature campaign pledge, but Democrats are adamantly opposed to giving him the funds.
The current closure of a quarter of federal agencies is the second-longest in history, leaving hundreds of thousands of government workers unpaid.
Aiming to keep up the pressure, President Trump will seek to rally ruffled Republican senators at Capitol Hill on Wednesday, before heading to the border on Thursday.
How did Democrats respond?
In a brief rebuttal, House of Representatives Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer demanded that Mr Trump end the shutdown.
Mr Schumer accused Mr Trump of trying to “govern by temper tantrum” and of manufacturing a crisis.
“President Trump has appealed to fear, not facts. Division, not unity,” the New York senator added.
He concluded: “The symbol of America should be the Statue of Liberty, not a 30-foot wall.”
Playing for time
Analysis by Anthony Zurcher, BBC News
There were two audiences for Donald Trump’s address to the nation on Tuesday night. The first was the American public, which polls indicate are generally uninterested in his border wall proposal and view the president as responsible for the government shutdown. The other was Republicans in Congress, who Mr Trump needs to keep in the fold if he is going to get anything out of this extended political confrontation.
It seems unlikely that the president said anything on Tuesday that will move the needle with the public at large. The arguments were familiar – and some have already been debunked. The president has been saying there’s a “crisis” at the border practically since he first started campaigning for president.
As for congressional Republicans, the speech was a demonstration that Mr Trump is going to use every arrow in his presidential quiver to get his wall. Tomorrow the president meets with his party members at the Capitol. On Thursday he travels to the border.
Already there are signs of cracks in the president’s support in Congress, however. The president, with his recent efforts, may have bought himself a bit more time for negotiations. It’s just not clear what good it will do him.
What would an emergency declaration achieve?
Though Mr Trump did not declare a national emergency on Tuesday night, analysts say he may still do so before the shutdown is resolved.
Such a dramatic escalation of the standoff might allow him to access military spending to fund his barrier, which remains un-built two years into his presidency.
But the president would be accused of usurping Congress’s constitutional power of the purse, and the move would be bogged down in a quagmire of legal challenges.
Some correspondents have speculated that he may ultimately resort to such a declaration as a last-ditch tactic to allow him to reopen the government without losing face to Democrats.
What’s the reality at the border?
Though both Democrats and Republicans agree there is a crisis at the border, critics have accused Mr Trump of greatly exaggerating the problem.
The number of illegal border crossings is down from 1.6 million in 2000 to fewer than 400,000 last year.
And research indicates that undocumented immigrants are much less likely to commit crime than native-born American citizens.
The White House suggested at the weekend that thousands of terrorists were caught attempting to cross the US-Mexico border, but in fact all but a handful were stopped at airports.