The bipartisan infrastructure deal senators brokered with President Joe Biden is hanging precariously ahead of a crucial Wednesday test vote as senators struggle over how to pay for nearly $1 trillion in public works spending.

Tensions were rising Tuesday as Republicans prepared to block the vote, mounting a filibuster over what they see as a rushed and misguided process. With Biden preparing to hit the road to rally support for his big infrastructure ideas — including some $3.5 trillion in a follow up bill — restless Democrats say it’s time to at least start debate on this first phase of his proposals.

“It is not a fish or cut bait moment,” said Senate Majority Leader Chuck Schumer, D-N.Y., describing the procedural vote as just a first step to ”get the ball rolling,” though Republicans say he is now downplaying the significance.

Six months after Biden took office, his signature “Build Back Better” campaign promise is at a key moment that will test the presidency and his hopes for a new era of bipartisan cooperation in Washington.

White House aides and the bipartisan group of senators have huddled privately since Sunday trying to wrap up the deal, which would be a first phase of an eventual $4 trillion-plus package of domestic outlays — not just for roads and bridges, but foundations of everyday life including child care, family tax breaks, education and an expansion of Medicare for seniors.

Biden calls it a “blue-collar blueprint for building an American economy back.”

Senate Republican leader Mitch McConnell and some outside groups decry what they call Biden’s “spending spree.” A core group of Republicans are interested in pursuing a more modest package of traditional highway and public works projects, about $600 billion in new funds, they have been trying to negotiate with the White House.

Biden has been in touch with both Democrats and Republicans for several days, and his outreach will continue “until he has both pieces of legislation on his desk to sign them into law,” White House Press Secretary Jen Psaki said Tuesday.

While Biden proposes paying for his proposals with a tax hike on corporations and wealthy Americans who earn more than $400,000 a year, the bipartisan group has been working almost around the clock to figure out a compromise way to pay for its package, having dashed ideas for boosting the gas tax drivers pay at the pump or strengthening the Internal Revenue Service to go after tax scofflaws.

Instead, senators in the bipartisan group are considering rolling back a Trump-era rule on pharmaceutical rebates that could bring in some $170 billion to be used for infrastructure.

Ten Republicans would be needed in the evenly split Senate to join all 50 Democrats in reaching the 60-vote threshold required to advance the bill past a filibuster to formal consideration.

Senate Republican leader Mitch McConnell and outside groups including the conservative Americans for Prosperity encouraged Republicans to vote against proceeding to the bipartisan package until they have more details.

“We still have a lot of work to do,” said Sen. Susan Collins, R-Maine, one of the members of the bipartisan group. “We’re making progress, but we need more time.”

Many Republicans are wary of moving ahead with the slimmer package, fearing it will pave the way for the broader $3.5 trillion effort Democrats are preparing to pass on their own, under special budget rules that only require 51 votes. Vice President Kamala Harris can break a tie.

McConnell said big spending is “the last thing American families need.”

“I think we need to see the bill before we decide whether or not to vote for it,” McConnell told reporters late Monday at the Capitol.

House Speaker Nancy Pelosi has been working to keep restless Democrats in her chamber in line, as rank-and-file lawmakers grow impatient with the sluggish Senate pace.

Liberal Democrats, in particular, are eager to make gains on Biden’s priorities — with or without Republicans.

“Time’s a wasting, I want to get this work done,” Rep. Pramila Jayapal, D-Wash., the chairwoman of the Congressional Progressive Caucus, told reporters Tuesday.

Jayapal warned against giving Republicans too much time to negotiate the deal away. “We have all the history in the world to show that this is what Republicans do time and time and time again,” she said.

Democrat John Yarmuth of Kentucky, the chairman of the House Budget Committee, said if the bipartisan effort fails, Democrats will simply include some the infrastructure spending in the broader package they are compiling with Biden’s other priorities.

Democrats hope to show progress on that bill before lawmakers leave Washington for their recess in August.

The legislative maneuvering marks a major test of Biden’s ability to deliver on a massive package of economic promises and reforms he made during his campaign.

Biden is making the case that America needs to make up for lost time with fresh federal outlays to shore up its aging infrastructure and households struggling to recoup from a shifting economy and the COVID-19 pandemic.

The economy has come back to life as more Americans have gotten vaccinated and Biden’s earlier $1.9 trillion relief package has coursed through the country. Employers have added an average of nearly 543,000 jobs a month since January, with Federal Reserve officials anticipating overall economic growth of roughly 7% this year that would be the highest since 1984. Yet there is also uncertainty as employers say they’re struggling to find workers at the current pay levels and inflation concerns have yet to abate.

(AP)