The White House is under increasing pressure to show progress on President Trump's $1 trillion infrastructure package.

While a detailed proposal isn't expected to land until later this summer, the administration plans to unveil a broad sketch of infrastructure "principles" before the end of this month and could reveal some of Trump’s rebuilding ideas in the president's budget proposal due out on Tuesday.The push to get out some details on one of Trump’s campaign promises comes as the president faces growing doubts on Capitol Hill about whether he will be able to muscle his infrastructure plan through Congress this year.

“The president, obviously, is very impatient,” Transportation Secretary Elaine Chao said during a Senate hearing last week.

One of Trump’s chief campaign promises was to upgrade U.S. roads, bridges, airports and other public works with a massive infrastructure proposal originally billed as a 100-day priority.

But the timeline has slipped as the White House and congressional leaders opted to first tackle healthcare and tax reform, neither of which have yet been completed. And now there is concern that Trump’s entire legislative agenda may be at risk, following a slew bombshell reports that have besieged the White House since Trump's stunning decision to fire FBI Director James Comey earlier this month.

Lawmakers and stakeholders have been clamoring for more details about Trump’s as-yet-unveiled infrastructure proposal, and transportation leaders have already held numerous hearings on the topic.

Chao assured members of the Senate Environment and Public Works Committee last week that the infrastructure plan has not been pushed to the back burner.

She said the administration will soon share a broad statement of principles that will help guide the infrastructure proposal and kick off Trump’s collaboration with Congress.

“I think they’re making real progress, but I do think they have a full plate, so they’re thinking we’ll put these principles out and follow it up with greater detail after July 4 or in September,” said Marcia Hale, president of Building America’s Future, a bipartisan coalition of elected officials focused on infrastructure.

But Chao warned that the principles have not yet been finalized, let alone key details like how the bill’s massive price tag will be paid for. She also said there will not be a list of specific projects in the package, as some had hoped.

Transportation advocates expect the list of infrastructure principles to be light on details, similar to a one-page summary of the administration’s tax plan that was pushed out just as Trump approached his hundredth day in office.

“It’s totally going to be a short summary,” said Norman Anderson, president and CEO of CG/LA Infrastructure. “But I don’t know if it’s a bad thing to get out a document of principles. I think it’s going to clear up a lot of confusion.”

That list of infrastructure principles isn’t the only marker that the White House is laying down.

On Tuesday, Trump’s budget proposal will reportedly call for $200 billion in federal funding over 10 years to upgrade the nation’s infrastructure. It’s also expected to include incentives to help encourage more private-sector investment.

White House press secretary Sean Spicer said the budget would mark the “first step” in Trump’s $1 trillion infrastructure push.

It’s unclear how the proposed boost for infrastructure would square with Trump’s March budget outline, which floated a 13 percent cut to the Department of Transportation and axed several transportation programs.

Even though the budget proposal is just a messaging document that won’t become law, transportation advocates think it would send a strong signal to stakeholders and Congress to include money for infrastructure.

“It’s a big deal,” Anderson said. “If you look at this budget, they’re going to slaughter a number of different areas. At the same time, putting in $200 billion [for infrastructure], that’s a big signal that President Trump’s commitment to infrastructure is real, at a point when people have been wondering.”

The budget release follows a tumultuous two-week stretch for the Trump administration, which has been scrambling to pivot from a string of controversies surrounding Comey’s abrupt firing.

Mounting tension over the investigations into Russian meddling in last year’s presidential election is just one roadblock that is threatening to derail Trump’s rebuilding initiative. The plan faces disagreements over funding offsets, has fiscal conservatives worried about the price tag and must find space on a packed legislative calendar.

Chao said that a detailed package won’t be unveiled until the “third quarter,” which would put it up against a trio of must-pass aviation, debt ceiling and spending bills.

"From a scheduling standpoint, yeah, it's going to be hard," Sen. John ThuneJohn Thune (R-S.D.), chairman of the Commerce, Science and Transportation Committee, told reporters this month.

"We've got to do the budget to do tax reform and finish healthcare first. And now the administration is saying they want to do infrastructure outside of tax reform, so it could, yeah, it could be something that gets pushed."

Several lawmakers who are anxious to deliver a win on infrastructure have been moving ahead with their own proposals in the absence of concrete details from the administration.

Sen. John Barrasso (R-Wyo.), chairman of the Environment and Public Works Committee, said last week that his panel is beginning to craft its own legislation and will work to ensure rural interests are included.

"We are going to work with the White House, but we're not going to wait," he said at a Transportation Construction Coalition event last week, according to Politico.

A bipartisan duo in the Senate introduced legislation that would leverage money from the private sector through a newly created investment bank to help make transportation upgrades.

And several groups of Democrats have unveiled their own robust rebuilding plans this year, including a recent House bill that would spend at least $85 billion on infrastructure improvements.

Rep. Bill Shuster (R-Pa.), chairman of the House Transportation and Infrastructure Committee, thinks the White House is "absolutely” feeling pressure from Congress to fulfill Trump’s infrastructure promise.

“The pressure is that a year from today, there is going to be 435 members of Congress running for reelection and 33 senators,” Shuster told reporters. “So they’d all like to go home and point to something and say, ‘Hey, we got something done.’”

By Melanie Zanona - 05/23/17 06:00 AM EDT