On Infrastructure, Bipartisanship Is Alive. On Jan. 6? Not a Chance.

Is President Biden about to achieve his holy grail?

A bipartisan deal on infrastructure appears to finally be in the offing, after a group of senators from both parties joined the president in the Rose Garden today to announce that they’d reached a compromise.

It’s far smaller than Mr. Biden’s original proposal, and some details remain to be worked out, but the president said that reaching any compromise at all was a major achievement.

“We have a deal,” Mr. Biden said, harking back to his days as a wheeler-dealer in the Senate. “I think it’s really important we’ve all agreed that none of us got all that we wanted.”

This follows on the heels of the Endless Frontier Act, a bill that aims to increase American competitiveness against China, which passed the Senate this month with broad bipartisan support. And in the House, lawmakers from both parties took steps this week to move forward with major antitrust legislation, signaling a potential breakthrough.

Six months into Mr. Biden’s presidency, is he about to deliver on the biggest — and arguably the most quixotic — promise of his presidential campaign: restoring bipartisan unity?

Not so fast. Just as Mr. Biden and the senators were taking their victory lap at the White House, Speaker Nancy Pelosi announced this morning that Democrats were forming a select committee to investigate the events of Jan. 6, a stark reminder that Republicans continue to block a bipartisan investigation into the violent uprising at the U.S. Capitol.

Ms. Pelosi said she was taking the step “with great solemnity and sadness,” arguing that she had been left with no choice.

And earlier this week, Republicans in the Senate united to shoot down a Democratic push to pass voting-rights legislation.

It appears that on matters with a blatantly political tint — and especially where former President Donald J. Trump’s shadow looms large, as it does on election laws and the Jan. 6 attacks — Republicans remain as unified as ever. But on other questions of policy, the battle lines may be slightly murkier, as the party continues to work out its own relationship with traditional fiscal conservatism after Mr. Trump’s right-wing-populist presidency.

Meanwhile, in the Senate, Democrats now face a challenge of their own: maintaining unity within their ranks as their most centrist members insist on slimming down their demands for progressive action. In a nod to the demands of his own party, Mr. Biden specified today that he wouldn’t sign the bipartisan package by itself: He plans to insist on receiving another bill, probably passed by Democrats alone, that will bring him closer to realizing the full breadth of his initial proposals on climate and infrastructure.

“If this is the only thing that comes to me, I’m not signing it,” Mr. Biden said. “It’s in tandem.”

Stephanie Cutter, a longtime Democratic strategist and adviser to Mr. Biden’s Building Back Together initiative, said that the process of passing two different bills would be potentially complicated and drawn-out. Still, she called the infrastructure deal a major win.

“We’re looking at the fall before this can come to a conclusion, but today is a big deal,” she said in an interview. “It’s the first time in a long time that Republicans have gotten on board with a Democratic president on a major piece of legislation.”

The political calculus in the Senate has significantly shifted since the early spring, when Democrats passed a $1.9 trillion relief bill without any Republican votes. The movement has been driven largely by Senator Joe Manchin III of West Virginia, who insisted that Democrats work together with Republicans on an infrastructure package rather than passing Mr. Biden’s ambitious proposals outright.

The deal that was announced today would cost $579 billion in new spending (and $1.2 trillion overall). That’s a small fraction of the $4 trillion that Mr. Biden had initially wanted to invest via his American Jobs Plan and American Families Plan.

The compromise leaves out most of Mr. Biden’s proposed investments in measures to confront climate change, or to support families and workers in the care industry.

To realize those, he would need to move a different piece of legislation. That would more than likely happen on a separate, Democrats-only track using the process of budgetary reconciliation, as Democrats did in March to pass their $1.9 trillion package.

“There ain’t no infrastructure bill without the reconciliation bill,” Ms. Pelosi recently told Democratic House leaders on a private call, according to reporting by The Times’s Emily Cochrane and Jim Tankersley.

The question for Senator Chuck Schumer, the Democratic leader, now becomes how to keep his own caucus united. He’ll have to keep enough progressives on board to pass the bipartisan bill — knowing full well that they may not get everything they want even if the Senate does turn around and pass a Democrats-only bill.

That second bill could include several of progressives’ top priorities, many of which are widely popular with the public but represent red lines for Republicans, including tax hikes for the wealthy, creation of green jobs and support for health care workers. But the relatively conservative Mr. Manchin would effectively have veto power on whatever went into that bill.

Mr. Manchin hasn’t signaled that he would support Democrats going big on their own, but he did indicate this week in an interview with NBC News that he would be open to passing some kind of “human infrastructure” legislation, paid for in part through tax hikes for the wealthy.

“Now, the size of the bill or what’s going to be done,” Mr. Manchin said, “the scope of that, we’ve got to find out.”

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