By Richard Cowan and Jeff Mason

WASHINGTON (Reuters) – President Donald Trump and senior Democrats failed to strike a deal in talks on Friday to end a partial shutdown of the U.S. government as they again fought over Trump’s request for $5 billion to fund his signature wall on the Mexican border.

After Democratic congressional leaders turned Trump down at a meeting in the White House Situation Room, the Republican president threatened to take the controversial step of using emergency powers to build the wall without approval from Congress.

Trump is withholding his support for a bill that would fully fund the government until he secures the money for the wall. As a result around 800,000 public workers have been unpaid, with about a quarter of the federal government closed for two weeks.

Senate Democratic Leader Chuck Schumer said Democrats had told Trump during the meeting to end the shutdown. “He resisted,” Schumer said. “In fact, he said he’d keep the government closed for a very long period of time, months or even years.”

Trump confirmed that comment but painted a more positive picture of the meeting, the first since a new era of divided government began when Democrats took control of the House of Representatives on Thursday.

“We had a very, very productive meeting, and we’ve come a long way,” Trump said.

But raising the stakes in his tussle with the newly emboldened Democrats, Trump threatened extraordinary measures to build the wall, which he says is needed to stem the flow of illegal immigrants and drugs into the United States.

NATIONAL EMERGENCY?

Asked by a reporter whether he had considered declaring a national emergency to build the wall, Trump said: “Yes, I have … I may do it … we can call a national emergency and build it very quickly.”

He said he could declare a national emergency “because of the security of our country, absolutely.”

The U.S. Constitution assigns Congress the power over funding the federal government so Trump likely would face legal challenges if he tried to bypass Congress on financing the wall. Building a wall – and having Mexico pay for it – was one of Trump’s main promises when he ran for president in 2016.

Trump’s wall project is estimated to cost about $23 billion.

Democrats have called the wall immoral, ineffective and medieval.

Nancy Pelosi, the newly elected Democratic speaker of the House, said Friday’s meeting with Trump was “sometimes contentious” but that they agreed to continue talking.

“But we recognize on the Democratic side that we really cannot resolve this until we open up government and we made that very clear to the president,” she said.

Credit rating agency Moody’s says the shutdown will cause minimal U.S. economic and credit market disruption but there could be a more severe impact on financial markets and the broad economy if the closure is protracted.

A Reuters/Ipsos opinion poll last week showed that 50 percent of the public blame Trump for the shutdown and 7 percent blame Republican lawmakers, while 32 percent blame Democrats.

In a Dec. 11 meeting with Pelosi and Schumer, Trump said he would be “proud” to shut the government over the security issue and would not blame Democrats. He has since said they are responsible.

Administration officials and congressional staffers are set to continue meeting over the weekend to try to end the impasse.

House Republican leader Kevin McCarthy told reporters that the leaders and Trump had decided to designate staff to work over the weekend. He said Trump had named Vice President Mike Pence, senior aide Jared Kushner and Secretary of Homeland Security, Kirstjen Nielsen.

The partial shutdown is straining the country’s immigration system, worsening backlogs in courts and complicating hiring for employers.

Federal agencies such as the Justice Department, Commerce Department and departments of Agriculture, Labor, Interior and Treasury have been hit by the shutdown.

House Ways and Means Committee chair Richard Neal, a Democrat, asked the Internal Revenue Service in a letter on Friday to explain the possible effects of the shutdown on the upcoming tax filing season for millions of Americans.

(Reporting by Richard Cowan and Jeff Mason; Additional reporting by Susan Heavey, Susan Cornwell, Tim Ahmann and Lisa Lambert; Writing by Alistair Bell; Editing by Bill Trott and Rosalba O’Brien)