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 the situation on the border was « a humanitarian crisis of the heart, and a crisis of the soul ».
The Republican president wants $5.7bn (£4.5bn) to build a steel barrier, delivering 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. »