Happy Infrastructure Week!

What became a punchline among political reporters during the Trump administration — when many a week was called “infrastructure week” by the White House, which was rhetorically committed to funding roads and bridges out of the federal purse — moved a step closer to reality on Wednesday, when the Senate voted to take up a $1 trillion infrastructure bill.

What exactly is and isn’t in the infrastructure bill? The Upshot has you covered.

But also important are the terms under which it was hashed out and by which it will pass into law, if it does pass into law. For this bill is bipartisan, shaped by a core gang of senators, five Democrats and five Republicans, who were backed by six more Republican senators as well as by the Biden White House. Not for nothing is it known as the Bipartisan Infrastructure Framework.

Wednesday’s vote over whether to proceed to debating the bill had the support of two-thirds of the Senate: all 50 Democrats and independents, plus 17 Republicans — including Mitch McConnell of Kentucky, the minority leader, who has famously said his goal was to deny President Biden and, before him, President Barack Obama any significant legislative victories.

The House of Representatives, where Democrats hold a slim majority, still must go along with it. A separate, decidedly partisan $3.5 trillion Democratic spending bill looms as a complication. But all in all, the infrastructure plan has come further than many had expected. Here is what political scientists who study legislative compromise (and the lack thereof) have to tell us about how this happened.

Why bipartisan laws are rare

It is a truism in national politics that the bipartisan legislative achievement is something people tell their grandchildren about with the wistful tone of the good old days.

Unlike a half-century ago — an era of Southern Democrats, Rockefeller Republicans and broad consensus (among white Americans, anyway) — today Democrats are liberal and Republicans are conservative.

“It’s hard to avoid the impact of what we call rising partisan polarization,” said Sarah Binder, a political science professor at George Washington University.

And in a polarized, two-party system, politics are zero-sum.

“If you think you’re a permanent minority, you come to the table and take half a loaf; and if you’re the governing party, you don’t mind,” Dr. Binder said. “But once you can see that your party has a very short window of control, you hold out for the whole loaf. And the opposition has to think: What is the cost if I just say no?”

No wonder that arguably the signature legislative achievements of the three most recent administrations — Mr. Biden’s Covid stimulus in March, Donald J. Trump’s tax cuts of 2017, Mr. Obama’s health care law — all passed the Senate on party-line votes.

The cross-aisle cooperation we get

But bipartisan legislation is passed. In fact, it happens all the time.

The ultimate liberal lion, Senator Ted Kennedy of Massachusetts, co-sponsored President George W. Bush’s signature No Child Left Behind law, and most other Democrats voted for it (including Mr. Biden, then a senator from Delaware); huge majorities of the Senate and the House voted for its reauthorization in 2015.

Mr. Obama passed the “fiscal cliff” compromise, extending various Bush tax cuts, with bipartisan majorities in early 2013.

And immediately after a resounding Democratic victory in the 2018 midterms, Mr. Trump’s criminal justice reform bill overwhelmingly passed both houses.

“Congress actually does try to do the public’s business, sometimes,” said John Aldrich, a professor of political science at Duke.

A popular genre of bipartisan legislation is the crisis response. The $700 billion bank bailout after the 2008 financial crisis passed the Democratic-controlled Senate and House with substantial Republican support before being signed by Mr. Bush. Last year, two gigantic stimulus laws related to the coronavirus pandemic were passed by a Democratic House and a Republican Senate, and then signed by Mr. Trump.

“Covid stimulus was bipartisan,” Frances E. Lee, a politics professor at Princeton, said. “They managed to do that in a presidential election year, after a presidential impeachment.”

The other kind of bill that often succeeds on a bipartisan basis belongs to what is sometimes called the Secret Congress. These bills touch on issues that do not arouse voters’ passions, usually because they are not seen as partisan.

“The policy area of the legislation is a crucial factor in whether it’s partisan or bipartisan,” said Ross Baker, a political science professor at Rutgers, who pointed to military funding and agriculture bills as examples.

Can the parties come together on infrastructure?

This brings us to infrastructure.

“It isn’t really ideological,” Dr. Binder said. “It doesn’t touch on social issues or cultural issues. It has the pretense of being paid for.”

She added, “Lawmakers tend to like voting for things that are popular.”

As Democrats’ proposals were winnowed down to the final compromise voted on yesterday, issues with partisan resonance, like in-home care and fighting climate change, fell by the wayside while issues with less salience, like airports and pollution cleanup, kept their funding.

Mitch McConnell, the man in the middle

This still does not quite answer why Mr. McConnell voted for the bill at this stage — or why the minority leader, usually able to corral most of his caucus to say no to a Democratic White House, stood by as Republicans negotiated.

Why hand Mr. Biden — who made achieving bipartisan results in Washington a central part of his pitch in last year’s presidential election — this victory? Another Republican leader has opposed this deal on precisely these grounds: “Who are these RINO” — Republican In Name Only — “Republicans that are so dedicated to giving the Radical Left Democrats a big and beautiful win on Infrastructure?” Mr. Trump said in a statement earlier this week.

Mr. McConnell’s ultimate instinct is for self-preservation, Dr. Binder said. The spate of bipartisan accomplishments under Mr. Obama came after the 2014 midterms, when Mr. McConnell had regained the majority but faced a tough slate of elections.

“He’s looking at 2016,” she said. “He has Republican moderates in Illinois and elsewhere in bluish states, so they finally redo No Child Left Behind, they do the last highway bill and some small-bore health care adjustments. It’s in the Republicans’ electoral interests that year to have something to run on.”

It worked. Though the Republican incumbent in Illinois, Mark Kirk, lost, ones in Pennsylvania, Ohio, Wisconsin, North Carolina and Florida won. Mr. McConnell lost two seats, but kept his majority.

The next time this particular slate of Senate seats is up for election is, yes, next year. Except the Republican incumbents in Pennsylvania, Ohio and possibly Wisconsin are not running for re-election, ceding a G.O.P. advantage. And Mr. McConnell cannot afford to lose two seats this time. In fact, he must net at least one to regain the majority.

“One of the reasons bipartisan bills are reasonably common is that the status quo, or what would happen if you didn’t pass legislation, is sufficiently bad,” Dr. Aldrich said.

“I think that’s a reasonable description of the politics of the infrastructure bill,” he added. “Trump won on it long ago. Part of the public dialogue is we actually need to do something about highways and core infrastructure. Republicans really felt they needed to do something.”

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