It was Monday night and the university football champions were coming to dinner at the White House. Catering staff were furloughed due to the partial government shutdown. So naturally Donald Trump served up a banquet of fast food. “Trump bought food from McDonald’s, Wendy’s, Burger King and Domino’s,” observed the late-night TV host James Corden. “Or, as he calls them, his four most trusted advisers.”

The US president’s widely mocked decision to splash out $3,000 of his own money said something about his obstinacy during the shutdown, now the longest in American history and the result of political stalemate over his demand $5.7bn for a wall on the US-Mexico border. As workers are hit in the pocket, airport queues grow and his poll ratings slump . It also raised the question: who are his real “most trusted advisers” and why are they urging him down a path to apparent political suicide?

The likely answer is a combination of the “Trump whisperer” Stephen Miller, an anti-immigration hardliner; the acting White House chief of staff, Mick Mulvaney, who has ideological reasons to shut down the government; rightwing media pundits and Trump’s own instinct to fight on an issue that he is being told will make or break his presidency.

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Miller, 33, and 51-year-old Mulvaney have filled the vacuum in an administration where endless staff churn has left moderate voices marginalized or expelled. The pair have seemingly gained the upper hand over potential restraining influences such as Vice-President Mike Pence and Trump’s senior adviser Jared Kushner.

Dan Cassino, an associate professor of political science at Fairleigh Dickinson University in Teaneck, New Jersey, said: “The anti-globalists are in the ascendant because there is no one else there.”

Miller helped torpedo a previous immigration deal between the president and congressional Democrats as well as a bipartisan effort during the Obama administration. He is Trump’s best-known speech writer, responsible for much of his inaugural address two years ago and currently working on his State of the Union speech for 29 January – itself jeopardized by the shutdown.

Republican leaders in Congress believed they had struck a deal to put off the battle over the wall for at least another month. But on 13 December, Miller appeared on Fox News to announce that the White House would take a stand to secure border wall funding.

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In an interview on CBS News, Miller described the wall as “a very fundamental issue” that would help determine “whether the United States remains a sovereign country”. Asked on CBS if “whatever is necessary” included a government shutdown, Miller replied: “If it comes to it, absolutely.”

Earlier this month, when Trump addressed the nation from the Oval Office to make his case for the wall and blame Democrats for the shutdown, the speech was quickly hailed as a Miller classic. The Atlantic magazine observed: “All of the tics and tropes of Millerian rhetoric were on display. The scary immigrants (“vicious coyotes and ruthless gangs”). The gory anecdotes (a veteran “beaten to death with a hammer by an illegal alien”). The decidedly un-Trumpian flourishes (“a crisis of the heart, and a crisis of the soul”).

Wendy Schiller, a political science professor at Brown University in Providence, Rhode Island, said: “Stephen Miller has become the singular voice on immigration in the White House. It does appear he has achieved the role he was blocked from by Steve Bannon, John Kelly and to an extent Jim Mattis. Now there is no one to block him.”

Mulvaney is another key influence on Trump. According to the Politico website, he spent much of the Christmas holiday with his boss at the White House, “egging on the president” in the fight with Democrats.

Facebook Twitter Pinterest Ann Coulter told Vice Trump was ‘dead in the water if he doesn’t build that wall’. Photograph: REX/Shutterstock

Chris Whipple, author of The Gatekeepers: How the White House Chiefs of Staff Define Every Presidency, commented: “If the reports are true, he’s really reinforcing all of Trump’s worst instincts. It is the job of the chief of staff to help the president govern; this is the opposite of that.”

A former Republican Tea Party and Freedom Caucus congressman, Mulvaney is a true believer in small government. As director of the Office of Management and Budget, he told reporters that “a good shutdown” might be necessary and could create the political climate “that fixes Washington DC permanently”.

Kurt Bardella, a political columnist and ex-spokesman and senior adviser for the House oversight and government reform committee, said: “Mulvaney was a Freedom Caucus member of the House and is now an extension of the Freedom Caucus in the White House. The entire crux of their philosophy is that government should be as small and limited as possible and so, in some ways, a government shutdown is a good thing.”

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The Tea Party wing was potentially emboldened when it forced a 16-day government shutdown over Barack Obama’s healthcare reform in 2013 yet did not pay a political price in the midterm elections a year later. And this time the Freedom Caucus may be tempted to consider a partial shutdown, affecting 25% of government, as a pain that can be tolerated, even though 800,000 federal workers missed their first pay cheques last week.

Schiller said: “If you get can away with running the government at 75%, you have an argument for trimming the government. They see it as a moment when they can persuade the American people that they can get by with less government.”

Miller and Mulvaney’s whispers into Trump’s ear are amplified by conservative media. When, in the week before the shutdown, the president seemed ready to accept a stopgap spending measure that would have kept the government open, there was a furious backlash from Rush Limbaugh, Ann Coulter and the hosts of Fox & Friends.

The Fox presenters Sean Hannity, Tucker Carlson and Lou Dobbs continue to pressure Trump to stand his ground, warning that he will otherwise lose the loyalty of his base and with it his hopes of re-election. Limbaugh said this week: “Trump is assuring everyone he’s not gonna cave on this, and I hope he doesn’t.”

Coulter told Vice News Tonight: “He is dead in the water if he doesn’t build that wall. Dead, dead, dead.”

It was the kind of argument that seems to be working on Trump. Even one of Fox News’s own political analysts, Juan Williams, said on air this week: “You should go listen to Sean Hannity, Rush Limbaugh and Ann Coulter, because they’re running this government. And they have forced this president into a trap.”

Cassino, the political science professor, said: “Fox News has been telling the president to stick to his guns and using the caravans in Central America as a chance to push that. We’ve also seen a lot of talk on Fox about Democratic divisions, suggesting that the Democrats are going to fold. Of course MSNBC and CNN are saying the opposite.”

Owned by Rupert Murdoch, Fox News has reduced coverage of the shutdown over the past two weeks, Cassino noted, while Hannity spent two nights bashing Trump’s election rival Hillary Clinton. “It suggests they’re playing it down and don’t see a way to make it positive for the president,” Cassino said.

Often Fox seems to be regurgitating Miller and Mulvaney’s talking points. Cassino observed: “It seems we have reciprocal causation. It’s hard to tell which is the dog and which is the tail. People in the White House know one of the best ways to influence the president is to get on Fox.”

Julian Zelizer, a professor of history and public affairs at Princeton University in New Jersey, suggested that Tea Party Republicans, Fox News, crowds at Trump’s rallies and his love of fighting were all contributing to the current impasse.

“He likes the drama of it: a president taking a heroic stand on television. It influences him and might even make him dig in more. He does not want to turn on TV and read a chyron saying he’s conceded. Then there are crowds he spoke to in the campaign. He’s talked about this wall and boxed himself in. He hears those voices in his head and doesn’t want to give in.”