Donald Trump’s plan to Make America Great Again is an unusual mixture of the traditional Republican avocations—cutting federal spending on the poor, privatizing government programs, fewer regulations, and massively regressive tax cuts—and a few populist economic proposals straight out of the Obama playbook. Central to Trump’s populist appeal is a trillion-dollar infrastructure plan, which the president-elect claims will create jobs and jump-start economic growth, but the former real-estate developer’s vision for a massive construction boom are already running into problems. For one, there are plenty of reasons to doubt whether his specific approach will be effective—critics point out that giving large tax credits to private investors would likely leave the country’s most needed repairs (like Flint’s water system) unaddressed, while pouring money into projects that are already profitable (like the electrical grid). Democrats, who ordinarily approve of increased fiscal spending on infrastructure, are wary to provide political cover to the Trump administration by backing his economic plan. And congressional Republicans, who spent the last eight years relentlessly attacking President Barack Obama over government spending, are reportedly worried about blowing a giant hole in the budget. Per Politico:

Key lawmakers say they’re in the dark on how Trump’s plan would work — with some conservatives simply hoping that his call for massive tax breaks will provide an economic jolt that makes the hard spending decisions easier.

Even congressional Republicans who have long championed spending on transportation projects say they don’t yet know the details of Trump’s 10-year proposal, which the president-elect has vowed will “put millions of our people to work” while making U.S. infrastructure “second to none.”

Despite their giddiness at the prospect of Trump rubber-stamping their agenda, some Republicans have started worrying about where the money is coming from, or how Trump’s plan would really work.

”Look, we don't have the details,” House Transportation Chairman Bill Shuster (R-Pa.) told POLITICO. “We're working very closely with his transition team and hopefully with the new department head to figure out how we're going to pay for it. It's got to be fiscally responsible.”

A trillion dollars is “a big number,” said Senate Commerce Chairman John Thune(R-S.D.), adding that a tax overhaul could be one promising way to pay for it. “I think it's going to come down to figuring out just actually what's achievable.”

Of course, Republicans have overcome their aversion to deficit spending before—the national debt soared during the Reagan years and under both Presidents Bush. The greater danger is for Democrats, who risk ceding credit for a massive public works program to the party that has traditionally fought against infrastructure improvements. Without his infrastructure plan, it’s not clear what would differentiate Trump’s economic agenda from the same slate of Republican policy proposals that have exacerbated the income gap in years past. But if he can pull it off, it’s possible Trump could transform his newly energized white voter base into an electoral powerhouse—or so Trump adviser Stephen Bannon hopes. “Like [Andrew] Jackson’s populism, we're going to build an entirely new political movement,” Bannon told The Hollywood Reporter last week. “It's everything related to jobs. The conservatives are going to go crazy.” Bannon’s reasoning, like Trump’s, is not so different than that of President Obama, whose advocacy for increased stimulus spending was repeatedly ignored by Republicans in the House and Senate. But this time, the Trump wing of the party hopes to use the same economic approach to consolidate the white vote into what Bannon calls “an economic nationalist movement.” Hypocritical or not, Democrats better hope Bannon’s master plan doesn’t succeed.