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 him of holding the American people hostage.
Both sides are trying to gain an edge amid an 18-day government shutdown.
The Republican president wants $5.7bn (£4.5bn) to build a steel barrier, which would deliver on his signature campaign pledge.
But Democrats - who recently took control of the House of Representatives - are adamantly opposed to giving him the funds.
The ongoing closure of a quarter of federal agencies is the second-longest in history, leaving hundreds of thousands of government workers unpaid.
What did President Trump say?
In an eight-minute address on Tuesday night carried live by all the major US television networks, Mr Trump said the federal government remained shut because of the Democrats.
He said of the situation at the border: "This is a humanitarian crisis, a crisis of the heart and a crisis of the soul."
Mr Trump said an as-yet-unratified revamp of the North American Free Trade Agreement would pay for the wall, a claim previously disputed by economists.
The president also said that 90% of heroin sold in the US came from Mexico, though US government figures make clear all but a small percentage is smuggled through legal points of entry.
Mr Trump correctly pointed out that Democrats have in the past supported a physical barrier.
In 2006, senators Chuck Schumer, Barack Obama, Hillary Clinton and Joe Biden voted in favour of 700 miles (1,120km) of fencing on the nearly 2,000-mile border under the Secure Fence Act.
Mr Trump cited cases of American citizens "savagely murdered in cold blood" by undocumented immigrants.
"How much more American blood will be shed before Congress does its job?" he asked.
On Wednesday, he will seek to stiffen the resolve of fellow Republicans on Capitol Hill before hosting congressional leaders for talks at the White House.
Mr Trump heads to the south-western border on Thursday.
How did Democrats respond?
In a brief rebuttal, House Speaker Nancy Pelosi and Senate minority leader Chuck Schumer demanded that Mr Trump end the shutdown.
Mrs Pelosi said: "The fact is the women and children at the border are not a security threat, they are a humanitarian challenge."
The California congresswoman added: "And the fact is President Trump must stop holding the American people hostage, must stop manufacturing a crisis, and must reopen the government."
Mr Schumer accused Mr Trump of trying to "govern by temper tantrum".
"President Trump has appealed to fear, not facts. Division, not unity," the New York senator said.
He concluded: "The symbol of America should be the Statue of Liberty, not a 30-foot wall."
Democrats argue that maintenance of existing border fencing, hi-tech tools to scan vehicles crossing at ports of entry, and hiring more personnel would be cheaper and more effective than a wall.
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