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Washington — Senators are drafting two large infrastructure bills after months of negotiations, but hurdles remain in bringing the bills to the floor ahead of August recess, when lawmakers will leave Washington for several weeks.

A bipartisan group of senators and their staff are finalizing the language for a nearly $1 trillion bill that primarily addresses surface transportation and “traditional” infrastructure priorities, as well as some climate-related provisions on electric vehicles, a deal that has the support of President Biden. But some Republicans outside of the team of core negotiators have raised concerns about how the package will be paid for, expressing skepticism about the proposal to fund part of it through tax enforcement.

Senate Majority Leader Chuck Schumer has said that he would like to bring the bipartisan deal to the Senate floor by the week of July 19, but it’s unclear whether the language of the bill will be finalized by then. The bill will need support from 10 Republicans along with all 50 Democrats to advance, and while 11 Republicans had previously suggested they would vote for the bipartisan proposal, some of them now seem to be getting cold feet.

“Pay-fors are still up in the air,” Senator Mike Rounds, a member of the larger group of Republicans that had agreed to the bill, told reporters on Tuesday. Senate Minority Leader Mitch McConnell has also not yet endorsed the bill, and his opposition could sink its chances.

Meanwhile, Democrats on the Senate Budget Committee are crafting a massive bill that could cost upwards of $3.5 trillion. This measure is intended to cover Mr. Biden’s priorities that are not included in the bipartisan bill, such as child care, health care, education and additional provisions to address climate change.

As this larger bill is unlikely to garner any Republican votes, Democrats are hoping to approve it using budget reconciliation, which would allow it to pass with a simple majority instead of meeting the typical 60-vote threshold to advance in the Senate. Senators must first craft a budget resolution, which will lay out instructions for passing the bill through reconciliation.

Senator Bernie Sanders, the Budget Committee chair who has suggested that the reconciliation bill could cost as much as $6 trillion, met with Mr. Biden at the White House on Monday. After the meeting, Sanders said he believed he and the president are “on the same page,” although he did not say whether the two had discussed a topline dollar amount.

“We are working really, really hard on this. And you’ve got 50 members of the Democratic caucus, and no great secret, some are progressive, some are more conservative. But I’m confident we are going to reach a happy medium and end up with a bill the American people can be very proud of,” Sanders told reporters at the Capitol after the meeting.

Senator Bernie Sanders talks to reporters outside the White House on Monday, July 12, 2021.

AP Photo/Susan Walsh

Sanders also suggested that the bill could cost more than $3.5 trillion, a number that had been floated by some Democrats as in line with Mr. Biden’s priorities.

“We’re going to fight for as large and as consequential a number as possible,” Sanders said.

Democrats on the Budget Committee met later on Monday evening, although they did not reach an agreement on how much the bill would cost. Schumer said that it was a “great discussion,” and that the committee Democrats would meet again on Tuesday night.

“We are making progress. Nothing to announce, but we’re making really good progress, and a lot of different viewpoints on the table, but I am I have been very optimistic about us getting to a good place,” Senator Tim Kaine told reporters after that meeting.