“The questions are in any infrastructure bill, but particularly if you’re going to do a big one: How big is the bill? How do you allocate it among priorities? … How do you finance it?” he said, nonetheless projecting optimism.

But the political obstacles Democrats face within their own ranks are growing like spring buds. Democratic moderates are flexing their muscle on Biden’s proposed corporate tax hike, while progressives have rolled out their own wishlist of long-sought social program expansions.

Democratic leaders in both chambers have worked for weeks behind the scenes to avoid tripwires as they prepare key portions of the bill, including a Tuesday meeting with Speaker Nancy Pelosi and her committee leaders. Many of the final decisions on the party’s infrastructure bill will still likely depend on their hardest-to-please members — Sens. Joe Manchin of West Virginia and Kyrsten Sinema of Arizona.

“All of these decisions still need to be made,” said Rep. Stephanie Murphy (D-Fla.), who leads the Blue Dog Coalition, a group of centrists who will be critical to passing the package in the narrowly divided House. “My hope is that it will yield a bill that is as bold as the votes will bear.”

Biden is also stepping up his outreach this week with key Democratic groups, including a sit-down with the Congressional Black Caucus on Tuesday, with the requests for the forthcoming infrastructure package continuing to pile up.

It’s not just ideological issues that could complicate Democrats’ path to even a party-line passage vote. A growing chorus of them are calling for changes in the tax code intended to give relief to blue states, revealing some policy dissension simmering between congressional Democrats and the White House.

“I think we’re building momentum and we’re continuing to build momentum,” Rep. Tom Suozzi (D-N.Y.), who organized the letter with Rep. Jerry Nadler (D-N.Y.), said in an interview Tuesday.

Sen. Angus King (I-Maine), who caucuses with Democrats, conceded that the SALT deduction could be an obstacle to getting the infrastructure bill through. “Certainly there are some members that are very concerned about it,” he said. “It directly and negatively impacted my state and other states.”

Restoring that deduction isn’t entirely a non-starter for the White House, but it would cost tens of billions of dollars a year, forcing compromises elsewhere. And those competing demands offer a glimpse at the months-long road ahead for Democrats as they draft another enormous bill that — unlike Biden’s first pandemic aid package — will be a complex, time-consuming unity test for party leaders.

The clock is ticking, and Democrats want to move fast, with the aim of passing Biden’s sweeping proposal, at least in the House, by the start of the August recess.

Congress returned to Washington this week for a legislative session that theoretically gives them time to answer the many remaining questions about Biden’s package, with leadership, committee chairs and key caucus groups all planning meetings on where to go next.

For now, Democrats say the plan’s three main pillars are in flux: the specific policy proposals, the pay-fors and the process.

“Number one: do we really want an infrastructure plan in Congress to pass — a bipartisan one?” said Sen. Jon Tester (D-Mont.). “Two: do we want to pay for it? Do we want to add to the debt? It’s going to be one or the other. And number three: What obviously classifies as infrastructure?”

The topic came up during Senate Democrats’ first in-person caucus lunch in more than a year. At the meeting, Senate Majority Leader Chuck Schumer encouraged members to find areas where they could work with Republicans on infrastructure, according to a senior Democratic aide. The Senate is expected to consider a bipartisan clean water infrastructure bill during this work period.

But Schumer also warned his caucus that they don’t have the luxury of time, given the Senate’s packed agenda, as well as the time needed to process nominations and appropriations before the chamber’s next recess in early May.

They also emphasize that Biden’s infrastructure plan is more of an outline rather than a concrete piece of legislation, requiring extensive work by Democratic leaders and committee chairs to turn it into a full-fledged bill.

“We feel a sense of urgency, but it’s not like the same time frame as the [Covid aid bill], where you could credibly claim that every day of delay meant preventable deaths,” said Sen. Brian Schatz (D-Hawaii.), who described the White House proposal as a “relatively loose framework.”

“These are investments that should stand the test of time, and therefore we’re going to have to engage the committees and do our work,” Schatz said.

One issue that does appear to be settled is Schumer’s push to pass legislation countering China’s influence. Schumer’s bill with Sen. Todd Young (R-Ind.), dubbed the Endless Frontier Act, was included in Biden’s infrastructure proposal. But the majority leader indicated on Tuesday that he intends to put the final product on the Senate floor this month, where it will be subject to a 60-vote threshold for passage.

“There’s enough bipartisan support that that should be able to go through a somewhat traditional format,” Sen. Ben Cardin (D-Md.) said of the China push, which has attracted several Republicans already.