Those obituaries for Trump-style populism? A bit premature.

There is no doubting why Donald Trump, America’s 45th president, chose to hang a portrait of Andrew Jackson, the seventh president, in the Oval Office: He sees himself as the political heir to the nation’s first populist president.

But that analogy has taken a beating. Last week, on one day alone, President Trump reversed himself on closing the Export-Import Bank, labeling China a “currency manipulator,” and canning Janet Yellen as chair of the Federal Reserve.

The “globalists,” including economic adviser Gary Cohn and son-in-law Jared Kushner, were ascendant; Steve Bannon, chief policy strategist and keeper of the populist-nationalist flame, was on the outs. Or so it seemed.

“What happened to America First?” asked Pat Buchanan, a godfather of Trumpism, in a column.

This week, Trump swung back to the protectionist roots of his campaign. He signed an executive order dubbed “Buy American, Hire American,” aimed at reining in the H-1B visa program, which he says takes jobs from Americans and drives down wages. Then he signed an order calling on the Commerce Department to determine if steel imports threaten national security. While he was at it, he took a slap at Canada over dairy imports.

Suddenly, Trump the populist is back. And Mr. Bannon clearly still has a seat at the table.

The test of governing

But taken together, the actions of Trump’s early presidency present a mixture of approaches that defy easy analysis. Campaigning with populist rhetoric is one thing, but governing as a populist presents a much bigger challenge, especially in the current US context, say experts on populism.

“Inevitably, you have to draw on people in the 'establishment' to fill your government, which of course Trump has done,” says Michael Kazin, a historian at Georgetown University and expert on social movements. “And you’ve got to deal with the different branches of government.”

To enact his agenda quickly, Trump would have needed large, supportive majorities in both houses of Congress and high approval ratings, and he hasn’t had those, Mr. Kazin adds.

Trump has relied on executive action, foreign policy maneuvers, and the bully pulpit to create a sense of momentum. But that will take him only so far. Next week, the home stretch toward Day 100 of the Trump presidency, will present another big test. Congress returns Monday with just five days to pass legislation that keeps the government running beyond midnight on April 28. And Trump is talking about trying again to repeal and replace the Affordable Care Act – an effort that failed a month ago.

"We have a good chance of getting it soon,” Trump said Thursday. “I'd like to say next week, but we will get it."

During the campaign, dismantling Obamacare was high on Trump’s populist to-do list. On Inauguration Day, his first executive order targeted the health-care law, allowing federal agencies to dismantle regulations. It wasn’t a repeal – that must be done by Congress – but it signaled a concerted effort to weaken the law.

Now Trump is back on the case. And he’s also still fighting against illegal immigration, against trade deals he sees as unfair, and for the US-Mexico border wall. Trump’s flip-flops have come more on international engagement – in his warm approach to China, his embrace of NATO, and his willingness to show US military muscle, particularly in his air strikes against the Syrian government and threats of action against North Korea.

In war, the saying goes, no battle plan survives contact with the enemy. And so it is with governing: There’s the roster of campaign promises, then there’s the reality of contact with Congress, where competing agendas – even from members of his own party – can make a president’s life miserable.

The Trump brand of populism

And what does it even mean to be a populist, in general and in Trump’s case?

“It’s a moving target,” says Ken Collier, a political scientist at Stephen F. Austin State University in Nacogdoches, Texas. “The problem with the populist label is it gets used so broadly. When you have a millionaire reality TV star claiming populist roots, that’s obviously a pretty specific strain of populism.”

Still, Mr. Collier says, Trump can pull it off. “Every generation will invent its own brand of populism,” he says. “I think maybe for this era, Trump can claim that label credibly.”

The proof, so far, is in Trump’s loyal following. His unwillingness to release his tax returns, charges of conflicts of interest over his and his children’s business dealings, and his lavish lifestyle – none have shaken his supporters’ faith in him.

Trump was elected to shake up Washington, and push back against the status quo. And even if he hasn’t had any breakthroughs in Congress, it’s still early – barely three months in.

Political historian David Greenberg sees in Trump the resurrection of a more precise meaning of populism. In recent decades, mainstream Democratic leaders could claim a certain level of populism in their calls for “fairness” in economic policy.

Among Republican leaders past, the populism came more in the cultural realm – in Richard Nixon’s appeal to the “silent majority” and in the more recent rhetoric against the “liberal Hollywood elite.”

'Something different'

But today, “I do think this tear-down-the-establishment kind of populism that seems in full force is something different,” says Mr. Greenberg, a professor at Rutgers University in New Brunswick, N.J. “It’s an important strain of American political thought that’s distinct from liberalism and conservatism.”

The parallel rise of Bernie Sanders, the independent senator from Vermont who challenged Hillary Clinton from the left during last year’s Democratic primaries, was clearly no accident. Senator Sanders and Trump often reinforced each other’s populism in their calls for fairer trade deals and focus on the working class.

Today, Sanders calls Trump a “right-wing extremist,” and not a populist, citing his attempts to repeal Obamacare and a budget plan that would cut nutrition programs for pregnant women and children.

As a candidate, Sanders bashed Wall Street with gusto. Trump has brought Wall Street with him to Washington, hiring top aides from Goldman Sachs and appointing the wealthiest cabinet in American history. Democrats will analyze Trump’s forthcoming plan for a “major tax reform” closely to see who reaps the most benefits.

And they may also ask, what would President Jackson, founder of the Democratic Party, think?

One can only guess. Even if Trump shares some common political traits with Jackson, their contexts are so wildly different. “If you let Andrew Jackson mingle with the crowds more, who knows what he would have said,” says Collier in Texas. “But it probably would have looked like a Trump tweet.”