WASHINGTON — The Senate on Wednesday cleared the first procedural hurdle toward enacting an expansive proposal to build and repair the nation's roads, bridges and broadband internet networks. But significant challenges remain.

The Senate voted 67-32 to open formal debate on the bipartisan infrastructure proposal. The procedural motion, which needed 60 votes, had support from 17 Republicans as well as 48 Democrats and the two independents who caucus with them.

After weeks of negotiation, the vote is a decisive victory for the first portion of President Joe Biden's “Build Back Better” infrastructure proposal.

According to the White House, the proposal would amount to the largest-ever federal investment in public transit, the largest investment in passenger rail since the creation of Amtrak and the largest bridge investment since the interstate highway system was constructed.

Despite wide bipartisan support for improving the nation's infrastructure, the bill, which is not yet completely written, will face further tests in the coming days as it goes through the Senate and later, when it goes to the House.

A separate, follow-on infrastructure bill that Democrats plan to push through without GOP support will likely be even more difficult.

Wednesday's successful vote to open debate on the bipartisan plan is no guarantee it will pass.

In addition to the risk of losing support from those Republicans who voted yes on Wednesday, a handful of Democrats have only committed to starting the process, and said they wanted to review the whole bill before agreeing to support final passage.

Sen. Mark Warner of Virginia, a lead Democratic negotiator, acknowledged it would not get every Democratic vote. “Anytime you do a bipartisan deal that doesn't go through regular order, people are understandably upset,” he said.

Sen. Kyrsten Sinema of Arizona, a moderate Democrat, told the Arizona Republic she would support starting the process on the bipartisan bill but still had concerns about the separate, second infrastructure bill Democrats planned to pursue without GOP support.

A previous attempt to start formal debate on the bipartisan plan failed last week when Republicans balked at Schumer's attempt to advance the bill before the final details had been hammered out.

Republicans who backed the proposal say that although they oppose Biden's broader infrastructure initiative — which includes improving health care and social safety-net programs — they support investing in the hard infrastructure projects, like roads and bridges.

“The need is dire,” said Sen. Rob Portman of Ohio, the lead Republican in the negotiations, citing 46,000 structurally deficient bridges in America.

The proposal includes $550 billion in new spending, down from $579 billion in prior drafts, according to Democrats and Republicans. Earlier drafts envisioned a total of $1.2 trillion in funds, after including the reallocation of previously approved spending.

Biden, touring a Mack truck plant in Pennsylvania on Wednesday, told reporters he felt “confident” about the emerging agreement.