President Joe Biden’s latest leap into the Senate’s up-and-down efforts to clinch a bipartisan $1 trillion infrastructure deal comes with even more at stake than his coveted plans for boosting road, rail and other public works projects.

The outcome of the infrastructure bargaining, which for weeks has encountered one snag after another, will impact what could be the crown jewel of his legacy. That would be his hopes for a subsequent $3.5 trillion federal infusion for families’ education and health care costs, a Medicare expansion and efforts to curb climate change.

Biden and Senate Majority Leader Chuck Schumer, D-N.Y., will need support from every Democratic moderate and progressive to push the $3.5 trillion bill through the 50-50 Senate, with Vice President Kamala Harris’ tie-breaking vote.

If the infrastructure talks implode, it may be harder for moderates — who rank its projects as their top priority — to back the follow-up $3.5 trillion plan, which is already making them wince because of its price tag and likely tax boosts on the wealthy and corporations.

“I would say that if the bipartisan infrastructure bill falls apart, everything falls apart,” West Virginia Sen. Joe Manchin, one of his chamber’s most conservative Democrats, warned reporters this week.

That could well prove an overstatement, since moderates like him will face enormous pressure from Biden, Schumer and others.

Biden met at the White House on Tuesday with Sen. Kyrsten Sinema of Arizona, a leader of moderate Democrats who’ve been laboring to strike an infrastructure deal with GOP senators. The president also used several tweets to prod lawmakers

White House press secretary Jen Psaki said Biden and Sinema “are very much aligned on the path forward” and expressed optimism, but also said the president was “not setting new deadlines” for a deal.

Moderate Democrats have long made an infrastructure deal their top priority.

If the infrastructure talks fail, it would deprive moderates of a victory that if reached might leave them more open to making concessions on the $3.5 trillion measure.

A collapse could also trigger fresh internal Democratic fighting over how much of the infrastructure spending would be transferred to the huge domestic spending plan, and how that would affect its overall price tag.

Even Republicans are divided over the infrastructure measure and what a failure of the bipartisan talks would mean as both parties eye 2022 elections in which House and Senate control are fully in play.

But others say that since Republicans won’t be able to stop Democrats from passing their $3.5 trillion bill, the GOP might as well back an infrastructure agreement.

Democrats plan to use special budget rules that would prevent Republicans from using a filibuster to derail the $3.5 trillion measure.

“I think it puts their members more on the defensive and having to defend very, in my view, indefensible spending and taxing,” said No. 2 Senate GOP leader John Thune of South Dakota.