A rail tunnel, left, at the Hudson Yards redevelopment site in New York. (Bebeto Matthews/AP)

Senate Democrats, emboldened by the GOP’s failure to unilaterally pass a health-care bill, are launching an effort to win bipartisan support for the investment of $500 billion in taxpayer dollars in infrastructure improvements.

With health-care changes at a standstill and tax reform — another objective on which Republicans campaigned last year — a complex project that is expected to take months, Democrats hope infrastructure spending will emerge as a desirable legislative win for Congress and the White House.

The Democratic push came in a week when President Trump appeared to acknowledge that his campaign promise to raise $1 trillion for infrastructure largely through private-sector investment was not feasible.

Democrats on the Senate Environment and Public Works Committee sent a letter Thursday asking to meet with Transportation Secretary Elaine L. Chao, reminding her of her confirmation-hearing promise to work in bipartisan fashion in delivering on Trump’s campaign promise.

That appeal is buttressed by an internal committee document in which the Democrats outline their infrastructure priorities for Chairman Sen. John Barrasso (R-Wyo.). Barrasso expressed worries at committee hearing in February that rural states like his wouldn’t attract much of the private investment Trump promised.

The committee’s Democrats spelled out a proposal to spend $500 billion more in tax dollars on infrastructure over 10 years, all in areas within its purview. (The committee’s domain is highways, the Banking Committee handles transit systems, and the Commerce Committee is responsible for buses and railways.)

With no more than a nine-page tax proposal on the table thus far, and divisions within the GOP that need resolution before a tax bill can pass, Democrats and many Republicans see an infrastructure funding package as something on which Congress can more readily agree.

“With health care, we have clearly seen that trying to rush through legislation on major, complex issues on a partisan basis is not a winning strategy,” said Sen. Thomas R. Carper (Del.), the Senate Environment and Public Works Committee’s ranking Democrat. “Senate Republicans should not make the same mistake on infrastructure, especially when we have an incredible opportunity to come together and do something historic that could positively impact every corner of this country.”

The decline of key systems — highways, water and sewer, the electrical grid, ports and levees along inland waterways — has been well documented, and state governments unable to keep up with repairs or expand when needed have communicated that to Congress.

With an abundance of bipartisan will to meet the need, the unresolved controversy has been how to pay for it. The options range from leaving much of the tax burden to the states, to increasing the federal tax on gas and diesel, to forcing multinational companies who have kept about $2 trillion in profits offshore to bring the money home, using the tax revenue from that money to pay for infrastructure.

But Congress, reluctant to approve anything that sniffs of a tax increase, has not opted for any of those options, or some combination of them. Instead, federal funding for transportation infrastructure has limped along with current revenue, boosted by funding that members of both parties have called “gimmicks.”

“We have woefully underinvested in our nation’s infrastructure for decades, and aging roads, highways, bridges, railways and waterways across our country show the consequences of those shortsighted decisions,” Carper said, echoing the findings of numerous studies. “If we make serious and smart investments in infrastructure, we could jump-start our local and national economy. We can’t afford to squander this moment.”

In a meeting with House Democrats on Tuesday, Trump reversed the position he campaigned on and enunciated at the outset of his presidency.

Based on a 10-page paper developed late in the campaign, Trump said he would stimulate $1 trillion in infrastructure expenditures over 10 years by granting $137 billion in tax credits to private investors.

The paper was the creation of Wilbur Ross, who now serves as commerce secretary, and Peter Navarro, who heads the president’s National Trade Council.

On Tuesday, however, Trump told Democratic members of the House Ways and Means Committee that luring private investors into a partnership with government was not the answer.

That change of stance surprised even those who had questioned whether private investors could meet all but a sliver of the need. Among those who supported the Ross-Navarro approach, the reaction was shock.

“I was both astonished and dismayed,” said Bob Poole, director of transportation policy at the libertarian Reason Foundation. “Everything the administration had said up until [Tuesday] was that public-private partnerships and private investments in infrastructure improvements was going to be the core of the program. There is not $1 trillion of federal money available.”