WASHINGTON (AP) -- Republican leaders in the House and Senate said Wednesday that they will reject Democratic demands for an immediate extension of health care subsidies, challenging Democrats to vote against a stopgap spending bill that doesn't include them but will keep the government open at the end of the month.

Senate Majority Leader John Thune, R-S.D., said Democrats "have a choice to make" as the Sept. 30 deadline approaches. They can work with Republicans, Thune said, or "they can shut down the government with all that will mean for the American people."

Democratic leaders have so far shown no signs of backing off their demands, arguing that it's Republicans' responsibility to negotiate with them as they will need at least seven Democratic senators to move the stopgap spending bill forward. It's a high-stakes game of brinksmanship for the Democrats, in particular, as the party's base urges them to fight harder and many wager that a shutdown would force Republicans to negotiate with them on health care and other issues.

"Democrats don't want a shutdown, but Republicans cannot shut Democrats out of the process and pretend like the last nine months have been business as usual," Schumer said.

It's a risky strategy. If the government does shut down on Oct. 1, most federal agencies will close and millions of federal employees deemed non-essential, including many in the military, won't receive paychecks. And there's no guarantee that the two parties could find agreement on how to end the standoff.

Democrats on both sides of the Capitol are watching Schumer closely after his last-minute decision in March to vote with Republicans to keep the government open. Schumer argued then that a shutdown would be damaging and would give President Donald Trump and his White House freedom to make more government cuts. Many on the left revolted, with some advocates calling for his resignation.

The vote in the spring caused a temporary schism with House Democratic Leader Hakeem Jeffries, who opposed the GOP spending bill and said he would not be "complicit" with Schumer's vote.

The two Democratic leaders now say they are united, and Schumer says that things have changed since March. The public is more wary of Trump and Republicans, Schumer says, after the passage this summer of Trump's "big, beautiful bill" that cut Medicaid and other government programs.

Democrats' top demand is that Republicans agree to extend health care tax credits that have made health insurance more affordable for millions of people since the COVID-19 pandemic. Thune and House Speaker Mike Johnson have indicated that they are open to extending the subsidies, which expire at the end of the year. The subsidies are available to low- and middle-income individuals who purchase health insurance through the Affordable Care Act. But many Republicans would like to see changes that most Democrats are likely to oppose.

Unbowed by the Democratic threats, House Republicans are moving forward with the stopgap measure to keep federal agencies funded through Nov. 21, buying lawmakers more time to work out their differences on spending levels. Republicans argue they are providing exactly what Democrats have insisted upon in past government shutdown battles -- a clean funding bill free of partisan policy riders.

"They're trying to insert unrelated matters into the middle of a clean government extension. And I don't think that's going to work," House Speaker Mike Johnson said on CNBC Wednesday morning.

The GOP bill would generally fund agencies at current levels, with a few limited exceptions, including an extra $88 million to increase security for lawmakers, the Supreme Court and members of the executive branch. The proposed boost comes as lawmakers face an increasing number of personal threats, with their concerns heightened by last week's assassination of conservative activist Charlie Kirk.

The House is expected to vote on the stopgap measure by Friday. Democrats said they would unveil an alternate proposal, but had not done so by Wednesday afternoon.

Trump, so far, has been dismissive of the Democrats' threats, saying last week to not "even bother" negotiating with them.

"If you gave them every dream, they would not vote for it," Trump said.

Democrats have tried to use those words against him and insist the president would take the blame if the government shuts down.

"Unless he's forgotten that you need a supermajority to pass a budget in the Senate, that's obviously his signal he wants a shutdown," said Wisconsin Sen. Tammy Baldwin, a Democrat.

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Associated Press writer Kevin Freking contributed to this report.