(BSS/AFP) - The agency responsible for safeguarding the US nuclear stockpile began placing most staff on enforced leave Monday, an official said, as yet another congressional vote to end the crippling government shutdown failed.

With the standoff about to enter its fourth week, some 1,400 workers at the National Nuclear Security Administration were due to receive notices telling them they had been placed on unpaid furlough.

"Due to the Democrat shutdown, approximately 1,400 NNSA federal employees will be furloughed as of today, October 20th and nearly 400 NNSA federal employees will continue to work to support the protection of property and the safety of human life," a Department of Energy spokesperson said in a statement.

The United States has an arsenal of 5,177 nuclear warheads, with about 1,770 deployed, according to the global security nonprofit Bulletin of the Atomic Scientists.

The NNSA, which oversees 60,000 contractors, is responsible for designing, manufacturing, servicing and securing the weapons.

The Department of Energy did not immediately respond to a request for comment, but CNN reported that the furloughs will initially hit sites that assemble nuclear weapons, such as Pantex in Texas and Y-12 in Tennessee.

At 20 days, the United States is enduring its longest full government shutdown ever -- the third-longest if partial stoppages are included.

President Donald Trump has been ratcheting up pressure on Democrats to vote with his Republicans to reopen the government, with increasingly ominous threats to slash public services and ramp up mass layoffs.

"So we`re hoping the Democrats become much less deranged and that we will get the vote pretty soon. And I hear they`re starting to feel that way, too," Trump said at the White House.

Kevin Hassett, director of the White House National Economic Council, told CNBC he expected the shutdown to end "some time this week" -- but he warned Democrats of "stronger measures... to bring them to the table" if it dragged on further.

- `Danger to the American people` -

Democrats` key condition for backing a House-passed funding resolution that would reopen the government through late November is the renewal of expiring health care subsidies for 24 million Americans.

Senate Republicans have offered a vote on renewing the subsidies, but many Democrats insist that any deal in the upper chamber will be meaningless without the sign-off of Trump and House Speaker Mike Johnson.

A Senate vote Monday evening on a House-passed resolution to reopen the government failed, for the 11th time.

Johnson has vowed to keep the House closed until the shutdown ends, and it has already been out of session since September 19.

"Every day that the government is shut down, it is a danger to the American people," Johnson told reporters on Monday when asked about the NNSA furloughs.

He warned that falling behind US adversaries in the nuclear arms race would be a "very serious" threat to the country`s status as "the last great superpower."

Trump has been clear that he believes Republicans are winning the messaging war and has not felt the need so far to intervene.

But Democratic strategists are confident that they can stick Republicans with the blame for skyrocketing premiums and health care coverage losses that would hit millions of Americans in 2026 if no action is taken.

"In Georgia, Virginia and Maryland, people are now finding out that their health insurance premiums are about to increase, in some instances by more than $2,000 per month, for a total of $24,000 per year," House Minority Leader Hakeem Jeffries told reporters.

"No one can afford those types of increases."

Federal employees -- who generally get paid every two weeks -- are expected to miss the entire amount for the first time on Thursday, and troop pay is another issue pressuring lawmakers to strike a deal.

The Senate is due to consider legislation midweek that would allow members of the military and other federal workers to receive pay, though it is not clear that the effort has sufficient Democratic buy-in.