Who is former Vice President Joe Biden trying to be to Democratic primary voters?

In the first debate, he was unapologetic in the face of criticisms of his civil rights record — and ineffective. He raised his hands along with his most progressive rivals in favor of leftward lurches on health care and immigration.

Since then, Biden has apologized for boasting of his ability to work with segregationists in the Senate. But elsewhere, he's tacked back to the center. He's come out against starting all over again on ObamaCare in the form of Medicare-for-all. He walked back his apparent endorsement of giving the same health-care benefits to undocumented immigrants and opposed decriminalizing illegal border crossings. Biden praised liberal darling Rep. Alexandria Ocasio-Cortez (D-N.Y.) but said "mainstream Democrats" win general elections. All while hugging former President Barack Obama tightly.

Some combination of the above makes sense. Biden has cornered the market on centrist Democrats, who remain far more numerous than online progressives would like to admit, while his opponents are clogging the left lane. While preserving that advantage, he also has to accommodate areas where the primary electorate has genuinely become more liberal. And he would be a fool not to play up his eight years alongside Obama, the first African-American president, who remains beloved by the Democratic base.

But adopting one persona, however shakily, in his first debate, grabbing another in his interviews afterward, while continuing a pattern of apologies and reversals that began with him abandoning his longstanding opposition to taxpayer funding of most abortions does not make Biden look like a confident and surefooted frontrunner. Biden has seen some slippage in the polls since that listless debate performance and is trying to right the ship. He nevertheless risks an identity crisis.

The massive Democratic field Biden sits atop may already be winnowing. While only one major candidate has dropped out — Rep. Eric Swalwell (D-Calif.) abandoned his campaign on Monday — most are polling at 1 percent or less. A four-way race between Biden, Sens. Bernie Sanders (I-Vt.), Elizabeth Warren (D-Mass.), and Kamala Harris (D-Calif.) is emerging, with Sen. Cory Booker (D-N.J.), South Bend, Indiana Mayor Pete Buttigieg, and former Texas Rep. Beto O'Rourke still having an outside chance.

It might not be possible for the former vice president to simply run out the clock. He is going to have to find a way to position himself in the Democratic race. And while being hero of the last administration, defender of civility, and competitor for the white working-class votes that went to Donald Trump in 2016 is not a bad start, ideology is going to have to play a role too. Harris has shown other Democrats that there is a political upside to taking on Biden in the debates, exposing some vulnerabilities — mainly using his long career in politics against him.

That's why if Biden's latest comments about Medicare-for-all mark the beginning of a new strategy of differentiating himself from the left, he is going to have to be ready to dig in and defend his position. He can't simply look toward the general election. Because there is a counterargument to Biden's pitch as the safe, electable candidate who can beat Trump: This was already tried four years ago by Hillary Clinton and Trump ended up winning.

Progressives will contend that in trying to win over the guy in the Midwestern diner, Biden will depress turnout among the base and once again fail to reunite the Obama coalition that made him vice president. Many of them believe it is now possible to win a national election running to the left of Obama himself. For his part, Trump seems to be getting ready to replicate his anti-Hillary campaign against Biden, a crime bill-supporting triangulator who backed the Iraq war and bad trade deals during decades of Washington in which Middle America's problems went unsolved.

Sound familiar? One bad debate won't sink Biden. Neither will a dozen faltering speeches. But if he loses either the electability argument or his lead with black voters, he is a frontrunner who can be overtaken. He does not have the overwhelming fundraising advantage normally enjoyed by a party establishment candidate. If Biden looks too desperate to keep ahead of the parade he hopes to lead, it will diminish his authority and gravitas.

Over two decades ago, another aging party elder sought to win a presidential nomination despite being an uneasy fit with ideological trends embraced by the next generation of leaders. "I"m willing to be another Ronald Reagan," Bob Dole told a group of Republicans, "if that's what you want."

Dole did win the nomination, even as several conservative challengers chipped away at his once formidable lead. But the end result of his presidential campaign — like Biden, his third — was not victory.