When candidate Donald J. Trump steamrolled American politics in 2016, he seemed to understand the coalition available to him was an eclectic bunch that felt its issues had been ignored.

They were both populists and conservatives, and they placed him in office.

Over the past week, it appears he has forgotten that his supporters are both populists and conservatives — with the “ and conservatives” being a very important part of the equation.

In the wake of an election where Republicans lost 40 seats, Trump has careened, strategy-free, toward a shutdown, negotiating only with himself. He's blowing up the staff that gave wary Republicans confidence, and in the realm of foreign policy, he's abandoning the Reaganite conservative part of his coalition to the consternation of Israel and the delight of dictators in Moscow and Ankara.

Trump won by bringing wary nationalists and populists into a conservative party. But the tail cannot wag the dog. Trump's coalition is big enough to govern as long as he agrees to preserve the four legs of the conservative stool: babies, guns, tax cuts, and a muscular foreign policy.

Republicans, of course, cannot win without populists. Trump understood that before anyone in the party hierarchy. But Trump cannot win without conservative Republicans — and the last month casts doubt on whether Trump understands that.

Coalition politics always requires sail-trimming by all coalition partners. Many Republicans who flocked to former President George W. Bush’s call to "restore honor and dignity to the White House" in the wake of the Bill Clinton-Monica Lewinsky scandal have swallowed hard and accepted Trump for the promise of conservative Supreme Court justices and the defeat of Democrats.

Now they wonder when Trump will trim his own sails for them.

The bargain has always been that he'd cut taxes and surround himself with traditional Republican foreign policy experts. The departure of Gen. Jim Mattis from the administration is not just a vacancy in the Cabinet. Coupled with United Nations Ambassador Nikki Haley's exit, this has Republicans, even those who have steadfastly stuck with the president, worried that there is a vacancy in the coalition bargain.

Trump has lost Senate Majority Leader Mitch McConnell, R-Ky., who bit his tongue for years, even as Speaker of the House Paul Ryan, R-Wis., spilled his spleen with frustrations over the president's lack of discipline.

Trump has also been publicly rebuked by Republican Arkansas Sen. Tom Cotton, perhaps the most populist and Trumpian member of the Senate but a foreign policy hawk nonetheless. An alienated Cotton and an angry McConnell, on top of the normal array of less steely handwringers, are not the building blocks of a strong coalition.

In 2008, candidate Barack Obama ran and won on a coalition that was made up of New Deal Democrats and the ascending coalition of young people, minorities, single women, and others. In 2012, he decided to shed the New Deal coalition and focus primarily on the coalition of the ascendant. He won but with less votes than he did in 2008, and it should be noted that his party, the Democrats, suffered deeply up and down the ballot under his new coalition.

The conservative populist coalition that Trump tapped into in 2016 was there long before he came along. Their impact was felt in elections they did vote in, like the 2010 and 2014 midterm elections, and also in the ones they didn’t vote in, like the presidential elections of 2008 and 2012, when Republican candidates John McCain and Mitt Romney did not inspire the populist portion and they stayed home.

Trump did not create this conservative/populist coalition. His presidency is the result of it. The past few weeks show he’s either forgotten that or he believes that doesn’t matter anymore.