There was, in fact, virtually no support within the Republican establishment for a Rockefeller run, just like there is very little support in the Democratic establishment for a Sanders presidency today. But that did not stop the New York governor from challenging his party, specifically on its platform, on issues ranging from defense spending (he wanted a lot more) to civil rights to medical care. And that challenge was one Nixon desperately wanted to avoid.

So, without consulting his advisers, Nixon sought a personal meeting with Rockefeller. It was granted, on terms that very much made Nixon look like a supplicant. He had to publicly ask for the meeting, which also had to be at Rockefeller’s Fifth Avenue triplex in Manhattan. And most importantly, when Nixon left the meeting at 3 a.m., he and Rockefeller had signed on to platform language that more or less repudiated Eisenhower and the Republicans across a range of concerns—especially on civil rights. On that issue, the compact’s strong language (“aggressive action to remove the remaining vestiges of segregation or discrimination in all areas of national life” and “support for the objectives of the sit-in demonstrators”) was admirable, but it undermined the tightrope Nixon was intending to walk between his party’s Northern liberals and its Southern whites.

The document—labeled “the Compact of Fifth Avenue”—was the political equivalent of a hand grenade. Conservatives, who carried a deep antipathy toward the deep-pocketed Eastern internationalist wing of the GOP that had denied them a presidential nomination for two decades, were furious Nixon had bent the knee to the symbolic leader of that wing. Some were angry enough to place in nomination the name of an emerging conservative hero, Senator Barry Goldwater of Arizona. Addressing the convention that summer, Goldwater said: “Let’s grow up, conservatives. … If we want to take this party back—and I think we can someday—let’s go to work.” Just four years later, Goldwater won the nomination before going down to a landslide loss in November to President Lyndon B. Johnson. The Republican Party did not adopt the Nixon-Rockefeller language on civil rights, but that language did cause Nixon a significant headache as he sought to replicate the gains in the South that Eisenhower, who carried Texas and Louisiana in 1956, had made in previous elections.

So what’s the lesson here for Biden? It’s that he needs to walk a fine line between respecting Sanders and his base and accommodating too many of their ideas, which Biden has explicitly opposed throughout the campaign.

When they were offered a clear, binary choice between Sanders and a less militantly left candidate, Democratic voters went for the relative centrist by significant margins. Seemingly out of nowhere, a broad coalition emerged—led by landslide majorities of African Americans—that that rejected the idea that a “political revolution” was the key to winning the White House. They support comprehensive immigration reform and protection for Dreamers—but they do not necessarily support free health care and college tuition for undocumented immigrants. They favor restoring voting rights for felons who have served their time; they do not necessarily support voting rights for felons who are still in prison. They favor expanded health care, but they do not favor a plan that would effectively abolish all private health insurance.

For the presumptive nominee of a party—which is what Biden is very close to becoming—there is a point where reaching out to unify the party crosses over into appeasement. Something like that almost happened in 1980, when Ronald Reagan came close to offering former president Gerald Ford the vice presidential slot on his ticket. Emissaries for Ford, including Henry Kissinger, were busily negotiating a range of duties for Ford that would have amounted (in Walter Cronkite’s words) to “something of a co-presidency”. It would have been a confession of weakness, a signal that Reagan doubted his own capacity for the job of chief executive. Luckily for the Gipper, the deal fell apart.

Biden should recognize the spirited campaigns Sanders has run, the passion of his followers and his achievement in forcing the Democratic Party to confront the nation’s yawning inequality, which requires major repair. And he should highlight his own ideas about increased taxes on the wealthy, criminal justice reform, and an ambitious health care plan that address some, but not all, of concerns of Sanders supporters.

But Biden also needs to act in a way that reminds his party and his country who is winning the most votes from Democrats and who will almost surely prevail when the convention assembles in Milwaukee.

One more point: When and if the two meet for an endorsement rally, it would be wise to hold it in Wilmington, Delaware, not Burlington, Vermont.