Speaker of the United States House of Representatives Mike Johnson has said that the current government shutdown could become the longest in history, as an impasse between the Democrats and Republicans drags on with no end in sight.

Speaking to reporters on Monday, Johnson, a Republican, said that he would not negotiate with Democratic lawmakers until they suspended policy demands related to healthcare, a dispute at the core of the shutdown.

“We’re barreling toward one of the longest shutdowns in American history,” said Johnson, who leads Republican lawmakers in the House.

The administration of President Donald Trump has used the shutdown, now in its 13th day, as a pretext for pushing forward a series of cuts and layoffs to government services and agencies, although its legal authority to do so remains in dispute.

Trump has plainly stated that such cuts will target his political rivals, saying last week that he would reduce “Democrat programmes” if the party refused to drop its demands on healthcare subsidies.

Meanwhile, the number of institutions affected by the shutdown continues to grow. On Sunday, the Smithsonian Institution, a federal trust that runs some of America’s most revered public facilities, including museums, libraries, research centres and the National Zoo in Washington, DC, said it had been impacted.

It announced that it was temporarily closing all 21 museums that it runs, along with research centres and the National Zoo. The institution depends on the federal government for 62 percent of its funding.

Recent polls have shown that US voters blame Democrats, Republicans, and Trump himself in roughly equal measure for the shutdown.

Democrats have called for an extension of subsidies under the Affordable Care Act that millions of people in the US rely on to buy healthcare plans.

Republicans have said that the issue can be addressed after the government is reopened, but Democrats have expressed doubt that the Republicans will honour that pledge.

Earlier this year, Republican lawmakers passed a huge tax and spending bill that is set to result in the loss of healthcare access for more than 15 million people.

While government shutdowns have become a routine occurrence in US politics in recent years, they can disrupt or reduce access to key services and force employees to work without pay for uncertain periods of time.

The US military said over the weekend that it would use unspent funds originally set aside for research and development to ensure that military personnel continue to receive pay.

The mass layoffs pushed by the Trump administration are a relatively new addition to shutdowns. Vice President JD Vance has warned that more “painful” cuts are ahead, even as government employee unions launch legal challenges against the terminations.