During the 2020 campaign, Joe Biden was outspoken in his desire to “revive the spirit of bipartisanship in this country.”

On May 15, Politico reported that, at the urging of many advisers, Biden had mostly given up on working with the GOP, which he purportedly now “views as an existential threat to the nation’s democracy.”

Four days later, Biden enjoyed the biggest bipartisan victory of his presidency. Talk about timing.

The historic $40 billion aid package for Ukraine was, as Senate Republican leader Mitch McConnell predicted, “a big bipartisan landslide.” Just shy of 80 percent of Republican senators voted for it.

Biden did “applaud the Congress for sending a clear bipartisan message to the world” in a written statement as he left for Asia. But he hasn’t boasted about delivering on his promise of bipartisanship.

Meanwhile, other leading Democrats think the real story is the Republicans who voted against the Ukraine package. “It is beyond troubling to see a growing circle of Senate Republicans proudly oppose Ukrainian funding,” Senate Majority Leader Charles E. Schumer said Thursday. “It appears more and more MAGA Republicans are on the same soft-on-Putin playbook that we saw used by former President Trump.”

Schumer has a point—the share of Republicans opposing Biden’s requests for support has grown; only three House Republicans objected to Biden’s initial statement of support for Ukraine in March.

But Schumer’s focus on the rump group that lost the vote illustrates why few in either party want to tout their bipartisanship. There’s very little incentive, particularly heading into the midterms, to brag about working with the enemy. The base just doesn’t want to hear it.

This has been a dynamic in Washington for a long time. When members of Congress work on a bipartisan basis, they like to do it as under the radar as possible, to avoid seeming like sellouts to the parties’ respective bases that see any compromise or collegiality as cowardly surrender.

Some call this the “secret” or “shadow” Congress. In an era of hyperpartisanship, if you want to get something done, the best thing you can do is not make a big deal about it. It’s a zero-sum calculation — if one party can declare a victory, the other party sees it as a loss. That’s both why Biden rarely boasts of the “bipartisan” in his “bipartisan infrastructure bill” win (officially the Infrastructure Investment and Jobs Act) and why the Republicans who voted for it have been treated like traitors by the base.

“All Republicans who voted for Democratic longevity should be ashamed of themselves!” Trump declared in November. That Trump desperately wanted an infrastructure bill when he was president shows how partisanship is a bigger priority than policy.

Still, in such a climate, one might wonder, why did Republicans overwhelmingly support the Ukrainian aid package? The most important, and obvious, reason is that it was necessary on the merits. A second reason is that a huge majority of Americans—including Republicans—support helping Ukraine any way possible short of sending troops. Republican approval of Biden’s handling of Ukraine is low, but that probably reflects Republican disapproval of Biden generally. Indeed, Republicans have often been more likely to say Biden has been too weak on Ukraine.

There’s a third answer that doesn’t fit a popular narrative among Democrats and many in the media.

Despite decades of hand-wringing to the contrary, the GOP is not an isolationist party, a fact Trump often learned to his consternation in the White House as he was forced to sign Russian sanctions and intervene militarily in the Middle East.

Even among the opponents of helping Ukraine, most argue that the U.S. should focus on confronting China instead, hardly an isolationist argument. Others hide behind newly discovered concerns about fiscal or procedural propriety. Sen. Rand Paul, a leading noninterventionist, claimed that he merely wanted an inspector general to oversee the spending of the aid money.

It’s true that there is a loud noninterventionist or “realist” bloc on the right, increasingly—and surprisingly—led by the Heritage Foundation and unsurprisingly by various instruments of the Koch network. But such efforts are hardly new, even if they are often treated that way.

Indeed, one might ask, why are Democrats so supportive of Biden’s effort? The most important answer to that question is the same for Democrats, too: It’s necessary and popular. But the fact that Biden is president is probably a big part of it as well.

After all, when Vladimir Putin seized Crimea, Democrats rallied to President Obama’s fairly tepid response. Partisanship works wonders.