WASHINGTON  – U.S. President Donald Trump on Thursday told Republican congressional leaders he will not sign a government funding bill because it fails to include enough funding for border security, raising the odds that parts of the federal government could shut down on Saturday morning.

Trump announced his decision during a closed-door meeting at the White House with a group of House Republican leaders, who afterward told reporters they would try to amend a Senate-passed bill to add $5 billion that Trump has demanded to go toward building a wall on the U.S. border with Mexico.

“We want to keep the government open but we also want to see an agreement that protects the border,” House Speaker Paul Ryan said on the White House driveway after meeting with Trump for more than an hour.

Earlier on Thursday, Trump had grumbled on Twitter that a version of the bill passed by the Senate on Wednesday failed to include the money for the wall, his signature campaign promise. But he had stopped short of threatening to veto the legislation, leaving open the possibility there would not be a shutdown.

Trump says a border wall is needed to keep out illegal immigrants and drugs but Democrats say it would be ineffective and wasteful.

His threat to hold up the bill is the latest plot twist in the long-running drama over government spending, and comes only 36 hours before funding expires for agencies responsible for federal law enforcement activities, airport security screenings, space exploration and farm programs.

It also came as lawmakers push to wrap up their work ahead of the Christmas break. Trump was expected to start a two-week vacation in Florida on Friday.

U.S. stocks, which were already sharply lower on the session, extended losses on the possibility of a shutdown, with the S&P 500 down more than 2 percent on the day.

Trump has said that he sees the border wall as a winning issue leading into his 2020 campaign for re-election. Last week in a White House meeting with Democratic congressional leaders, he said he would be “proud to shut down the government for border security.”

The Senate bill approved on Wednesday had provided a seven-week extension of existing funds for agencies, punting the funding issue into the next Congress.

PUSH FROM THE RIGHT

But hard-right conservative pundits and lawmakers had urged Trump to push for border wall funding now, even if it leads to a shutdown, arguing that it would be impossible to get once Democrats take control of the House on Jan. 3.

“He (Trump) campaigned on the wall,” Republican Representative Mark Meadows said. “It was the center of his campaign … the American people’s patience is running out.”

The House Rules Committee was to meet later on Thursday to determine how to add the $5 billion in an amendment to the Senate bill, its chairman, Pete Sessions, told reporters.

If the House fails to pass the amendment, it is unclear whether Trump would sign the funding bill, Sessions said. “We’re all putting that in the calculator,” he said.

Representative Steve Scalise, the No. 3 Republican in the House, told reporters that his members also would try to add funding for states hit by recent natural disasters.

House Democratic Leader Nancy Pelosi has said including border wall money in the bill would be a “non-starter” for her members. They were, however, open to the disaster aid, she said.

If the government goes into partial shutdown starting Saturday morning, it could last until the new Democratic majority takes over in the House in January. Then it will have enough votes to pass a funding bill to send tot he Republican-controlled Senate, leaving it up to Trump to decided whether to veto it.

Meantime, Trump administration officials were looking for ways to build the wall by reassigning money already doled out to U.S. agencies for other projects.

The White House has not provided details of that effort but leading Democrats have warned that shifting funds around in such a way would have to be approved by Congress.

During his 2016 campaign Trump repeatedly said Mexico would pay for the border wall but never specified how. Last week he said that a new trade deal his administration had negotiated with Mexico and Canada would generate enough savings to be equivalent to Mexico financing the wall.

Money for the wall also led to a partial government shutdown during a weekend in January and a second funding gap in February lasted only a few hours. Impact on government services was negligible in both cases.

The most serious government shutdown came in 2013 when conservative Republicans made an unsuccessful effort to use funding bills to repeal President Barack Obama’s healthcare law.