After Ronald Reagan, then 73, faltered in his 1984 debate with Walter Mondale, he got off the canvas and delivered one of the great knockout punches in history. Asked about his age in the next debate, he said, “I am not going to exploit, for political purposes, my opponent’s youth, and inexperience.” Even Mondale laughed.

Reagan added, “It was Seneca, or it was Cicero—I don't know which—that said, ‘If it was not for the elders correcting the mistakes of the young, there would be no state.’”

It was Cicero, and he was right. The past informs the present.

It remains to be seen whether Joe Biden, 76, can recover from his flop. After a strong campaign launch, Biden did what Biden does; he became his own worst enemy, and inarticulately opened the door for Kamala Harris by invoking his willingness to work with segregationists in the 1970s.

What he was trying to say was that you can't always use the steamroller of ideological purity to get where you want to go. One must consider the realities of the terrain ahead, and sometimes that involves negotiating with unsavory characters. LBJ's advances on civil rights are one example, and before him, Lincoln. You don't get to choose the players on the field. You have to weigh the options of working with or against them.

That doesn't sit well with the all-or-nothing crowd who insist on using a microscope to reexamine the past without acknowledging context. They see the tree but miss the forest. Ideology makes for great speeches. Pragmatism's about understanding the topography.

Biden's failing was being unprepared for Harris' calculated takedown. It was a bit of an 'Et tu, Brute?' moment, but this isn't a coronation. He could have emulated Pete Buttigieg, who took responsibility for failing to integrate the police force in South Bend; instead, Biden tried to defend a weak, archaic position. Contrition is rare in politics, but it can be effective. It redeemed Reagan after Iran-Contra. It could have done the same for Biden.

His out-of-touch unsteadiness was unsettling for centrists who see the country careening into an authoritarian, plutarchian abyss. They just want a candidate — any candidate — who can win and restore normalcy. They've concluded that any one of the Democratic hopefuls possesses more humanity than the president, who has buried the ethical bar so deep, nightcrawlers can slither over it.

Harris, an establishment Democrat, proved something with her dismantling of Biden—that she could do the same to Trump. However, if the left wing of the party insists on living or dying with Bernie Sanders or Elizabeth Warren, it might well be the latter. Their messages resonate with many, the messengers, perhaps not as much. With eyes fixed on the shining light of ideological purity above, it's easy to step into the mud. Sanders purists may have denied Hillary Clinton more votes than Putin did.

An ideological litmus test, letting the perfect become the enemy of the good, could doom America to four more years of Trumpism. Or worse.

This is triage. First, you stop the bleeding.