The impending departure of President Trump’s top White House adviser on infrastructure, DJ Gribbin, is being cast by critics as further proof the administration’s much-touted initiative has stalled.

But White House officials have quietly been engaged in negotiations on Capitol Hill, and the administration insists it is moving ahead on its infrastructure package.

At a rally in Ohio last week, Trump acknowledged the lack of Democratic support for what he had promised would be a bipartisan effort, saying his proposal would “probably have to wait until after the election” in November.

Many Republicans in Congress have also been unenthusiastic about the 10-year, $200 billion proposal, which the Trump administration said would prompt $1.5 trillion in overall spending, an idea dismissed by outside economists. Last year’s business-oriented GOP tax cuts left little fiscal room for what candidate Trump said would be a signature project to rebuild America.

White House officials, led by Gribbin’s deputy Alex Herrgott, have spent the past few months negotiating with Republicans and a handful of Democrats on the Hill, according to a participant in the talks who spoke on the condition of anonymity to talk frankly.

They are working to devise authorizing legislation that would leave the question of how to pay for the package until later, and GOP leadership is aiming to mark up the bill in May, the participant said.

“The whole idea is to figure out the policy first,” the individual said, and sort out a funding mechanism later.

Democrats have publicly called for reversing some corporate tax cuts to pay for $1 trillion in federal spending to begin meeting what some officials say is $4 trillion in infrastructure needs, although that proposal was quickly rejected by administration officials.

There also is a looming shortfall of more than $120 billion in the Highway Trust Fund, a major source of road and transit spending, with no agreement on how it should be addressed. Many Republicans and Democrats also are at odds over a push to roll back environmental rules the administration says are slowing projects.

Gribbin was a key architect and vocal defender of Trump’s plan, which calls for $100 billion in federal incentives to spur state, local and private spending, plus tens of billions more for rural development and other “transformative” projects.

A date for Gribbin’s departure has not been given, but a replacement will be named, a White House official said. Herrgott, the White House Council on Environmental Quality’s associate director for infrastructure, is a top contender, but a final decision has not been made.

Critics say Gribbin’s midstream exit points to broader problems.

“It’s another in a series of signs that show how unserious the administration is about doing infrastructure in a real way,” said a senior Senate Democratic aide who also spoke on the condition of anonymity to talk freely.

A White House official denied that the personnel change signals the initiative is going nowhere.

“That’s simply not true,” said the official, who would describe the administration’s position only on the condition of anonymity. Trump stands behind the plan, which was shaped by his appointees across the federal government, the official said.

“It’s the president who is its chief advocate,” the official said. “As long as he’s around, infrastructure will continue to be a priority, and he will continue to call on Congress to move his plan forward.”

The White House official also said, “DJ’s departure was entirely his decision.”One congressional aide, who was not authorized to speak on the record, said of Gribbin: “The job he’s had to do in the last 15 months has been pretty thankless. For his own sanity, I’m not surprised at all” that he’s leaving.

At a speech last month to the American Association of State Highway and Transportation Officials, Gribbin, a former executive at Macquarie Capital who has worked for Koch Industries and the Transportation Department, defended the administration effort.

“One of the most amazing parts about this job is you put these ideas out there and it’s unbelievable how far people can get” from those actual proposals to their interpretations of them, Gribbin said. “It’s amazing. Where did you get that from? There’s a Wharton study. . . . Did you read what we put out? Like, I have no idea how you got to where you got.”

Economists at the Penn Wharton Budget Model said the Trump plan would, under their most generous interpretation, lead states and others to spend just $30 billion more on infrastructure overall, beyond the $200 billion from Washington. That is in contrast with the more than $1 trillion predicted by Gribbin and other administration officials.

The Wharton economists said states and localities would spend less of their own money on projects, a well-established phenomenon known as substitution. The administration points to its proposed incentive grants, which require $4 in state or local spending for every $1 in federal money, as well as other programs.

But the Wharton economists, citing decades of academic research, said numerous administrations have tried to mandate that local spending continue at the same pace, despite federal infusions — and failed.

Beyond Trump’s $200 billion proposal, the $1.3 trillion bipartisan spending bill Congress passed last month includes billions more for roads, bridges, airports and transit and water projects.

Some congressional Democrats described the increases as a repudiation of Trump’s approach.

Trump’s budget proposals, for instance, called for eliminating an Obama-era Transportation Department grant program known as Transportation Investment Generating Economic Recovery, or TIGER, which has funded projects ranging from a highway in Lincoln, Neb., to a main-street improvement project in Akron, Ohio.

Instead, Congress tripled the TIGER program to $1.5 billion from $500 million.

Trump administration officials offered an upbeat interpretation.

“It’s not the exact way we would have done it, but it accomplishes many of the goals we had,” said Deputy Transportation Secretary Jeffrey A. Rosen.

Rosen said there were wins for the administration, including blocking what he said was an effort to give undo advantage to major tunnel and bridge projects connecting New Jersey and New York, known as the Gateway Program.

“Any language giving preference to that was turned off, and we were happy to see that,” Rosen said.

That project is a priority of Senate Minority Leader Charles E. Schumer (D-N.Y.), with whom Trump has sparred despite their shared history as New Yorkers.