During his victory speech last week, President-elect Donald Trump devoted more than a single sentence to just one piece of policy. It wasn’t a border wall or immigration, nor trade, nor even Obamacare. Instead, the very first specific promise Trump made upon claiming the presidency was to follow through on the one issue that united him and Hillary Clinton—and divided Republicans in Washington: infrastructure.

“We are going to fix our inner cities and rebuild our highways, bridges, tunnels, airports, schools, hospitals,” the president-elected pledged. “We’re going to rebuild our infrastructure, which will become, by the way, second to none. And we will put millions of our people to work as we rebuild it.”

For Democrats, the high billing for one of their top priorities was a faint silver lining in a devastating night. “We can work together to quickly pass a robust infrastructure jobs bill,” Nancy Pelosi, the House minority leader, said in her own statement on the election results. She followed up with Trump on a congratulatory call the next morning, her spokesman said, telling him that infrastructure was one area where they could “find common ground.”

While Trump’s support for increased investment in infrastructure attracted much less attention than his signature proposals for a wall along the Southern border and a ban on Muslims entering the country, the Republican actually said he would spend more than “double” the $250 billion in direct spending proposed by Clinton.

Trump’s bigger challenge will be to persuade congressional Republicans that they should revisit an idea they belittled as pork-barrel spending when a Democratic president-elect, Barack Obama, proposed it as his first priority eight years ago. Whether House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell accede to Trump’s demand—and whether he relents if they don’t—will go a long way toward revealing just who is in charge of the new Republican-dominated political order in Washington.

In the week since the election, Ryan and McConnell have said quite a bit about working with Trump to repeal the Affordable Care Act, secure the border, and reduce regulations. They have said nothing at all about infrastructure. “He’s not really laying out next year’s agenda. We still have a lame-duck session to get through,” McConnell spokesman Don Stewart wrote in an email on Monday. Ryan spokeswoman AshLee Strong was similarly noncommittal. “House Republicans are only just beginning to talk with President-elect Trump and Vice President-elect Pence about the agenda for 2017,” she said. “Speaker Ryan intends to continue these discussions with the transition team.”

To get a sense of Ryan’s pre-election view of the infrastructure question, however, consider his response when The Atlantic’s Ronald Brownstein asked, during the Washington Ideas Forum in late September, whether he would help Trump pass “a $550 billion, or more, infrastructure program.” Ryan laughed loudly and slapped his hand on the arm rest of his chair. “That’s not in the ‘Better Way’ agenda,” the speaker replied, referring the six-point plan he and other House GOP lawmakers unveiled earlier this year as their campaign platform. “Just so you know, we just passed the biggest highway bill since the 1990s.”

After years of delays and stopgap bills, Congress did approve a six-year, $305 billion highway bill last December, but the Obama administration and advocates for infrastructure investment considered the legislation woefully short of the amount needed to bring the nation’s roads and bridges into good repair. Before the 2009 stimulus, infrastructure had enjoyed mostly bipartisan support on Capitol Hill. But while there remain a solid number of Republican lawmakers who want to increase spending on transportation and other upkeep, the hurdle in recent years has been finding a way to pay for it. Congress has not raised the gas tax in more than two decades, and ideas to finance infrastructure in other ways have not gone far.

Advocates are hoping a new Republican administration can succeed in winning over conservatives where Democrats could not. “I have seen a sea change in the attitudes on the Hill,” said Marcia Hale, president of Building America’s Future, a bipartisan advocacy group whose co-chairmen include former Transportation Secretary Ray LaHood, a Republican, former Democratic Pennsylvania Governor Ed Rendell, and ex-New York Mayor Michael Bloomberg. “I wouldn’t say everybody’s supportive, but there’s been a big change in attitude. People now recognize we need to do something.”

“Where it becomes problematic is what do we need to do, and how are we going to pay for it?” Hale said. “Is it difficult? Yes. Is it possible? I think so.”

Details of what Trump has in mind are scarce, and his presidential transition website includes just two paragraphs on transportation and infrastructure. It is mostly platitudes except for a number: $550 billion. The Wall Street Journal reported that Trump’s advisers want the money to come largely from private financing backed by tax credits. Hale said private financing could be part of a successful package but that public investment was also needed. Clinton’s plan combined about $250 billion in direct spending with another $25 billion devoted to creating a national infrastructure bank that could leverage up to $250 billion more in investment through loan guarantees.

Conservatives outside of Congress are watching the talks warily, but in a sign of just how much Trump’s election has shaken up the political dynamic, they have not dismissed the idea of a big infrastructure bill out of hand. They are even resuscitating what was once a dirty word on the right.

“My guess is you will see a massive stimulus package from the Trump administration,” said Adam Brandon, chief executive of FreedomWorks. “However, it’s going to be 180 degrees different from what we saw before. I believe it’s going to be more tax-based stimulus. It’ll be more regulatory-relief based stimulus.”

Brandon said he was open to an idea both Democrats and Republicans have discussed in recent years known as repatriation: encouraging corporations to bring back cash they have parked overseas by offering a one-time lower tax rate. The immediate boost in tax revenue would then go to creating an infrastructure bank. “If you can use this repatriation cash for this purpose, I think you’d see that would sit well with conservatives,” Brandon said. “If it’s just straight debt for projects, I think that would sit poorly with folks.”

That kind of proposal also won support from Representative Dave Brat, the Virginia conservative who ousted then-House Majority Leader Eric Cantor in 2014 and has since been a critic of Paul Ryan. Like Brandon, he said he could support an infrastructure bill if the decisions about which projects to fund were made outside of D.C. “Bring back $2 trillion from abroad. Use some of that for infrastructure,” Brat told me before the election. “Try not to run it through the federal government so that actually something happens. If we can do that, that’s great.”

Repatriation alone is not likely to bring in the $550 billion that Trump wants to spend, and whether he accepts the conservative version of an infrastructure program might not be known for several months. But advocates like Hale are convinced he is serious about the problem if for no other reason that, unlike so many others he will inherit, it is what he knows.

“He’s a builder. He’s a developer. This is an issue he really, really understands,” Hale said. “And he’s about to, as any president is, be confronted with an enormous amount of issues, and this is his comfort zone.”

“I do think the president-elect wants to do this,” she added, “and I would suggest he’s probably going to get his way on some things.”