President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE will unveil his long-awaited proposal to rebuild the nation's infrastructure next month, a White House official told The Hill on Thursday.

Trump will release "detailed legislative principles" in early January, the official said, delivering on a longstanding promise to invest in America's infrastructure. Trump had vowed during the 2016 campaign to invest $1 trillion in infrastructure projects, though the issue has taken a backseat to other GOP priorities in Congress this year.

But the White House has been working behind the scenes to craft a detailed, 70-page infrastructure memo. The document, which will be submitted to Congress next month, will likely serve as the building block for lawmakers to write actual legislation. ADVERTISEMENT The administration has long said it wants to use $200 billion in federal seed money, along with significant permit reform and other incentives, to leverage $1 trillion worth of overall infrastructure investment.

The president indicated in late November that the White House would move on to infrastructure after the Republican-led Congress passed the GOP tax reform plan.

Republicans are expected to iron out differences between their tax bills in the coming weeks after the House passed its plan last month and the Senate passed its version late last week.

“We’ll be submitting plans on infrastructure … soon after taxes,” Trump said in November at the White House.

House Transportation and Infrastructure Committee Chairman Bill Shuster William (Bill) Franklin ShusterLobbying firm cuts ties to Trent Lott amid national anti-racism protests Ex-Rep. Frelinghuysen joins law and lobby firm Ex-Rep. Duffy to join lobbying firm BGR MORE (R-Pa.) told The Hill after emerging from Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE's (R-Wis.) office Wednesday that he had discussed infrastructure with leadership, another sign that the rebuilding initiative could be imminent.

Critics of the Trump administration say that passing an infrastructure bill is unlikely after the White House missed an opportunity to link it directly to the tax-reform bill.

“If they’d taken up infrastructure, we’d have a bill today and have the money to fund it,” said former Rep. Ray LaHood (R-Ill.), who helmed the Department of Transportation under President Obama.

“Nothing happened this year, so the prospects of anything happening next year I think are pretty slim," he said.

The White House scrapped plans earlier this year for a council of outside advisers to help the Trump administration craft an infrastructure bill.

And while there is wide consensus on Capitol Hill about the need to upgrade crumbling U.S. infrastructure, there is far less agreement over how to pay for it.

One of the potential infrastructure offsets – international tax reform – is instead being used to pay for the GOP tax package.

Rep. Ted Yoho Theodore (Ted) Scott YohoKat Cammack wins Florida GOP primary in bid for Ted Yoho's seat The Hill's Convention Report: Democrats gear up for Day Two of convention Eyes turn to Ocasio-Cortez as she seeks to boost Biden MORE (R-Fla.), a member of the far-right House Freedom Caucus, said on Thursday that lawmakers are "kicking around" a new funding idea, though he declined to elaborate.

"It's outside of the box thinking," Yoho told The Hill.