Republicans cleared the first hurdle in avoiding a government shutdown on Thursday night.

The House of Representatives seemed poised to pass a bill to keep the government open until 16 February, after promising conservatives a vote on a major increase in defense spending, a hard-line immigration bill as well as other unnamed concessions that the conservative House Freedom Caucus leader Mark Meadows called “subplots” on Thursday night.

However, this legislation would likely be dead on arrival in the Senate, where Democrats have said they have enough votes to block the legislation. But, by passing the House, it would allow Republicans to attempt to shift the blame for a potential government shutdown to Democrats.

Quick Guide All you need to know about a US government shutdown Show What is a government shutdown? When the US Congress fails to pass appropriate funding for government operations and agencies, a shutdown is triggered. Most government services are frozen, barring those that are deemed “essential”, such as the work of the Department of Homeland Security and FBI. During this shutdown, around 25% of the government workforce is placed on unpaid furlough and told not to work. Workers deemed essential, such as active duty military personnel, are not furloughed. Why might the government shut down? The president and members of Congress are at an impasse over what should be included in a spending bill to keep the government open. How common is a shutdown? There have been more than a dozen government shutdowns in the US since 1981, although ranging in duration. The longest occurred under Bill Clinton, lasting a total of 21 days from December 1995 to January 1996, when the then House speaker, Newt Gingrich, demanded sharp cuts to government programs such as Medicare, Medicaid and welfare.

This shutdown is on course to be the longest in US history. What would be the cost of a shutdown? A government shutdown would cost the US roughly $6.5bn a week, according to a report by S&P Global analysts. “A disruption in government spending means no government paychecks to spend; lost business and revenue to private contractors; lost sales at retail shops, particularly those that circle now-closed national parks; and less tax revenue for Uncle Sam,” the report stated. “That means less economic activity and fewer jobs.” Hundreds of thousands of people are not receiving regular paychecks in this shutdown. In previous shutdowns, furloughed employees have been paid retrospectively – but those payments have often been delayed. Sabrina Siddiqui Photograph: Win McNamee/Getty Images North America

An impasse would result in Donald Trump marking his first anniversary in office with the first government shutdown in four years, even though his party controls Congress. In the event of a shutdown, most government services would freeze and most federal workers would go unpaid.

Negotiations over the budget stalled in recent days, amid a dispute over spending priorities and immigration.

The breakdown of talks kicked off a pre-emptive blame game in Washington, with Trump and Republicans pointing a finger at Democrats for insisting that any compromise include protections for nearly 700,000 young undocumented immigrants brought to the US as children.

“We’ll see what happens,” Trump told reporters during a visit to the Pentagon on Thursday. “It’s up to the Democrats.”

The president’s decision to stop by the US Department of Defense, as Republican leaders in Congress crafted a contingency plan in the event of a shutdown, underscored the political urgency.

There has never been a government shutdown, which would cost the US an estimated $6.5bn a week and stifle economic progress, when one party has controlled both chambers of Congress and the White House.

At the Pentagon, Trump sought to pit Democrats against the military by claiming a shutdown would have the worst impact on the defense department.

While most government services are frozen during a shutdown, national security work that is deemed “essential” continues to operate. The majority of federal employees placed on unpaid furlough are non-defense employees. Active duty military personnel are not furloughed.

Earlier Friday, the president unexpectedly undermined a short-term plan offered by House Republicans. The stopgap measure would push the funding deadline to 16 February and, in an attempt to sway Democrats, reauthorize a popular children’s health insurance program for six years.

But as the House prepared to vote on the measure on Thursday, Trump criticized the bill, tweeting: “CHIP [the Children’s Health Insurance Program] should be part of a long term solution, not a 30 Day, or short term, extension!”

Hours later, the House speaker, Paul Ryan, downplayed divisions between Republican leaders and the White House. “I spoke with the president. He fully supports passing what we’re bringing to the floor today,” Ryan said.

Fiscal conservatives had expressed frustration that the bill would represent the fourth short-term extension since October, when funding for the government was first due to expire. Congress has since passed a series of stopgap measures to keep the government running in the absence of a longer-term deal. However, the concessions made to conservatives on Friday night were sufficient to get enough wavering right wingers to back another short-term bill.

Democrats in the lower chamber were largely unified in their opposition to the Republican bill, with the House minority leader, Nancy Pelosi, likening it to “a bowl of doggy doo” in a Thursday press conference on Capitol Hill.

The bill’s fate looked similarly uncertain in the Senate, where Republicans hold a slim 51-seat majority and would need at least nine Democrats to support the plan.

A handful of swing state Senate Democrats announced their opposition to the House bill, citing its failure to address a number of funding priorities. Democrats said a short-term fix would delay critical funding for the opioid crisis, as well as emergency relief for areas in Florida, California and Puerto Rico left devastated by storms and wildfires last year.

Democrats remain primarily concerned with extending protections to the young, undocumented immigrants, known as Dreamers, who were left in limbo when Trump rescinded Barack Obama’s 2012 Deferred Action for Child Arrivals (Daca) policy in September.

The Daca program protected hundreds of thousands of Dreamers from deportation with temporary legal status. Trump gave Congress until 5 March to enact a replacement, but Democrats have argued legislation on the controversial issue of immigration is unlikely to pass unless tied to a must-pass bill such as funding for the government.

Bipartisan discussions on immigration were also severely undermined last week when the president made derogatory comments in a private meeting, about immigrants from countries such as Haiti and El Salvador. According to lawmakers in attendance, Trump questioned the need for the US to accept immigrants from “shithole countries”.

On Thursday, Chuck Schumer, the Democratic leader in the Senate, said Trump “doesn’t give a hoot if the government shuts down”.

“The White House has done nothing but sow chaos and confusion, division and disarray,” Schumer said in a Senate floor speech.

“And it may just lead us to a government shutdown that nobody wants; that all of us here have been striving to avoid.”