A key House committee next week will begin the slow process of turning President Trump's aspiration of a $1 trillion infrastructure initiative into reality.

Trump renewed his campaign call for a massive push to update the nation's roads, bridges, public transportation systems, pipelines and ports during his address to Congress last month, but so far has not sent any type of proposal to Capitol Hill.

Although a pet issue of Trump's, the White House and congressional leaders have agreed to make the drive essentially third in their list of priorities, after repealing the Affordable Care Act and rewriting the tax code.

But the House Transportation and Infrastructure Committee will start the process on Wednesday by hearing from state and local officials about how to improve the nation's surface transportation system and streamline the way the federal government helps encourage and fund surface transportation projects.

Trump gathered a handful of business leaders, entrepreneurs and even one environmental advocate at the White House this week to begin sketching out his vision for rebuilding the nation's infrastructure, which reportedly includes high-speed rail, according to the Wall Street Journal, which was permitted to attend the private Oval Office meeting.

He also is focused on the "shovel-ready" type of projects Democrats and President Barack Obama promised to prioritize with 2009's stimulus package.

"We're not going to give the money to states unless they can prove that they can be ready, willing and able to start the project," Trump said at the meeting. "We don't want to give them money if they're all tied up for seven years with state bureaucracy."

Administration officials have met with key lawmakers to broadly discuss his initiative, but no member of Congress attended the Wednesday meeting.

During his address to Congress, Trump asked lawmakers to "approve a $1 trillion investment in the infrastructure of the United States." Since then, House Transportation and Infrastructure Committee Chairman Bill Shuster, R-Pa., has made clear that giving Trump what he wants is not tantamount to the federal government footing the bill.

"It's not going to be a trillion dollars coming out of Washington, D.C.," Shuster said at an American Association of State Highway and Transportation Officials conference in Dallas this month. "There obviously has to be more money coming out of Washington, D.C. But there are billions and billions of dollars out there today, private sector dollars that are going to be spent."

One major existing source Republicans can tap is the highway bill, a five-year authorization for federal contributions to road and infrastructure projects nationwide Congress approved last year.

Beyond that, it becomes less clear how much the federal government will actually spend and from which source the funds will come.

The idea of a repatriation tax holiday that could raise $200 billion has been floated, as has the possibility of new royalties from increased drilling on public lands that could generate $1.5 trillion in tax dollars.

But there is still no clarity on how to finance it, especially without adding to the national deficit, a perquisite of many conservative lawmakers such as members of the House Freedom Caucus.

There is also disagreement over timing. Shuster is dedicated to moving something year, but there are rumors that Trump is fine with letting it slip to next year.

It's the one GOP priority that can attract significant Democratic support. House Democratic Leader Nancy Pelosi, D-Calif., on Thursday called on Trump to leapfrog it to the top of his to-do list.

"Democrats believe the greatest nation in the world should have the best infrastructure in the world," Pelosi stated. "But instead of rebuilding America's infrastructure, the president is busy destroying Americans' health coverage. The Trump Administration and the Republican Congress should abandon their assault on healthcare and work with Democrats to forge a bipartisan path forward on job-creating infrastructure projects across America."