WASHINGTON >> President Donald Trump blew up Republican strategies to keep the government open past Friday when today he said a long-term extension of the popular Children’s Health Insurance Program should not be part of a stopgap spending bill pending before the House.

He wrote on Twitter: “CHIP should be part of a long term solution, not a 30 Day, or short term, extension!”

With a possible government shutdown looming this weekend, the House had planned to vote late today on a stopgap spending bill that would keep government funding flowing to Feb. 16 as delicate negotiations continue to protect young, undocumented immigrants brought illegally as children from deportation.

But by midday today, the chances of a shutdown appeared to be rising. Virginia’s two Democratic senators, Mark Warner and Tim Kaine, whose constituents include hundreds of thousands of federal workers, announced together that they would oppose the stopgap spending bill. They had been seen as among the most likely yes votes in the Senate, where Republican leaders need at least nine Democrats to support the bill.

“Congress should remain in session with no recess until we work out a long-term bipartisan budget deal that addresses all issues,” Warner and Kaine said in a joint statement.

The president’s tweet only added to the confusion. Republican leaders had spent Wednesday pressuring Democrats to vote for the spending bill, arguing that opposing it would effectively block a six-year extension of the children’s health program, attached to the spending bill as a sweetener for lawmakers in both parties.

Speaker Paul D. Ryan of Wisconsin said on Wednesday that it would be “unconscionable” for Democrats to oppose funding for CHIP with a “no” vote on the short-term spending bill.

Hours after Trump’s tweet, the White House tried to walk it back. A White House spokesman, Raj Shah, said that the president supports the House’s stopgap bill.

But Democrats pressed their advantage. Sen. Chuck Schumer, D-N.Y. and the minority leader, brought up the tweet and questioned whether it meant that the president opposes the stopgap measure that congressional leaders from his own party are trying to pass.

“Who knows?” Schumer asked. “It’s a mess.”

Despite Trump’s tweet, Republican leaders appeared committed today to keeping the children’s health funding in the stopgap bill.

Ryan said he had spoken to Trump earlier in the morning and that the president “fully supports passing what we’re bringing to the floor today.”

Sen. Mitch McConnell, R-Ky. and the majority leader, continued to press Democrats to support the stopgap bill, citing their professed support for extending funding for the Children’s Health Insurance Program.

“I’m more than puzzled why they would threaten to turn their backs on those children and shut down the government while they’re at it over the entirely unrelated issue of illegal immigration,” McConnell said.

Even if the House manages to pass the bill, the Senate would still need to give its approval in order to avert a shutdown early Saturday morning, and Democrats will be needed to overcome an expected filibuster.

The extension of CHIP funding is important for Democrats, who have strenuously complained that federal funding for the program was allowed to lapse last fall.

But this week, Republicans have postured as the champions of CHIP, which began under President Bill Clinton.

“I feel that it makes no sense for Democrats to try and bring us to a shutdown, to try and cut off CHIP funding for the states that are running out of money, like Minnesota and Washington and Kentucky and other states,” Ryan said.

McConnell also highlighted the CHIP funding as he expressed hope that Democrats would support the stopgap bill.

“The Democrats in the Senate have been very consistent in clamoring for addressing the children’s health care program,” McConnell said on Wednesday. “This does it with a six-year reauthorization. They claim they don’t want to shut down the government, so it seems to me it would be a rather attractive package. I certainly hope that’s the way they look at it.”

But Democrats are under heavy pressure to oppose any spending bill that does not protect the young immigrants, known as Dreamers, who are now shielded from deportation from an Obama-era initiative that Trump rescinded.

If the stopgap bill passes, Schumer said, “there will be no incentive to negotiate, and we’ll be right back here in a month with the same problems at our feet.”

With his tweet, Trump even inadvertently backed late-night talk show host Jimmy Kimmel in his fight with House Republicans over their use of CHIP as a lure to win Democratic votes despite the impasse on immigration. Kimmel responded by saying that Trump was “absolutely correct.”

Why the president suddenly undercut Republican arguments was not immediately clear. On Wednesday, the Trump administration released an official statement endorsing the stopgap measure, including the extension of funding for CHIP.

Aside from the sudden debate over children’s health care, the fate of the stopgap measure still seemed uncertain because of resistance within the House Republican conference. Most House Democrats are expected to oppose the bill.