Government shutdown updates: Leavitt says Trump exploring cutting aid to Portland

The federal government officially entered a shutdown at 12:01 a.m. Wednesday amid an impasse on Capitol Hill over competing congressional spending bills.

A Democratic-backed spending bill that would also extend health care subsidies under the Affordable Care Act and reverse cuts to Medicaid failed in a last-ditch vote on Tuesday.

A GOP-backed stopgap bill that would have funded the government for the next seven weeks also fell short of the needed 60 votes just hours ahead of the deadline.

President Donald Trump and Republicans have cast blame for the shutdown on Democrats' health care demands, while Democrats insist Republicans need to negotiate.

As the clock ticked toward a funding lapse, White House Office of Management and Budget told federal agencies to begin preparing their plans for an "orderly shutdown."

An estimated 750,000 federal workers could be furloughed each day the federal government remains closed, according to the Congressional Budget Office. While many workers deemed essential -- such as air traffic controllers, airport security officers and some members of the military -- will remain on the job, they will not be paid until after the shutdown ends.

The Trump administration has threatened mass layoffs of some federal workers during the shutdown.

Senate Minority Leader Chuck Schumer urged Republicans to come to the negotiating table after the upper chamber failed to pass a measure to avert a government shutdown that is now just hours away.

"We want to sit down and negotiate, but the Republicans can't do it in their partisan way, where they just say it's our way or the highway," Schumer said at a news conference following Senate votes Tuesday night.

Pressed on what the Democrats' strategy is to get Republicans to negotiate, Schumer said, "The strategy is the American people are demanding it and are going to demand it more and more on Oct. 1 [and] Oct. 2."

Schumer rehashed the failed votes on the Senate floor -- placing the blame on Republicans who "have failed to get enough votes to avoid a shutdown."

Asked if he can guarantee with 100% certainty that the GOP's short-term continuing resolution would not reach 60 votes in another round of votes, Schumer carefully responded, saying, "Look, the bottom line is, as I said, our guarantee is to the American people that we're going to fight as hard as we can for their health care, plain and simple."

He said the GOP-backed seven-week stopgap measure is "totally partisan" because "there was no input from Democrats."

Schumer stood firm on Democrats’ health care demands, calling for extending Affordable Care Act subsidies and reversing Medicaid cuts.

"The bottom line is, we need to stop these premiums from going up dramatically. We need to do it now, not in October, when people get the notices; not in November, when they have to decide whether to drop health care or reduce the health care they get," he said.

-ABC News' Lauren Peller

Senate Majority Leader John Thune said Republicans are now on the hunt for a few additional Democrats to support their "clean," short-term funding bill after three Democrats defected during a vote on the GOP-backed measure earlier Tuesday.

Sens. John Fetterman, Catherine Cortez Masto and Angus King (an independent who caucuses with Democrats) voted with Republicans on a short-term funding bill aimed at keeping the government open for seven more weeks.

Speaking at a press conference Tuesday night, Thune said he intends to bring that bill forward for a vote again on Wednesday -- and he said he believes more Democrats might be willing to support it.

"There are others out there, I think, who don't want to shut down the government but who are being put in a position by their leadership that should make them -- ought to make all of them -- very uncomfortable," Thune said. "So we'll see."

Republican Sen. Rand Paul voted against the Republican bill. But with the multiple Democratic defections, Thune said Republicans will continue their efforts to get enough Democrats on board to pass the short-term funding bill.

Thune said Senate Republicans need eight Democrats total to vote for the measure to ensure passage.

"We are going to have some more votes and we will see where the Democrats come down. I hope we have enough to change their minds and we can keep this government open and responsive to the American people," Thune said.

-ABC News' Allison Pecorin

The Senate adjourned for the night Tuesday -- with no remaining paths to keep the government open past 12:01 a.m. Wednesday.

The Senate is expected to vote again on Wednesday, likely on the same two measures that failed Tuesday -- a seven-week stopgap bill backed by Republicans and a Democratic-backed bill that extends Affordable Care Act subsidies.

Neither bill got the required 60 votes to pass.

-ABC News' Allison Pecorin