President Biden on Monday took a subtle yet unmistakable dig at Republicans who have backed away from a major funding component in a bipartisan infrastructure package that is now starting to fray, saying pointedly that “we shook hands on it” even as he continued to promote the agreement.

Biden’s comment, with its accusatory undertones, reflected the agreement’s precarious state at the outset of what could be a pivotal week. Senate Majority Leader Charles E. Schumer (D-N.Y.) plans to force a vote within days to advance the roughly $1 trillion plan despite the Republican hesitations, a high-stakes gamble that is intended to force agreement but that GOP senators on Monday warned they would reject…

The current flare-up revolves around more than $100 billion in revenue that a bipartisan group of senators hoped to raise by beefing up Internal Revenue Service enforcement so it could better collect unpaid taxes. Conservatives rebelled against empowering an agency they deeply distrust, however, even after Republicans including Sen. Rob Portman of Ohio, a top GOP negotiator, sought to address the concerns by proposing safeguards on the IRS’s authority.

But those suggested restrictions made the IRS provision virtually unworkable, according to aides familiar with the discussions, forcing negotiators to nix it as a source of revenue and leaving senators scrambling to find tens of billions of new dollars to pay for the infrastructure deal.