Former Vice President Joe Biden will enter the first Democratic presidential debates with 19 rivals taking aim at him — nine on the night he will be onstage, 10 the night he won't be there to defend himself. He is the clear-cut frontrunner and his party's two dozen other White House aspirants have no choice but to try to take him down.

So far, the attacks on Biden's boast that he was able to work with segregationist Democrats of old — an awkward example of civility to offer an increasingly woke party — seem to have fallen flat. In the latest Morning Consult poll, Biden leads by double digits nationally and wins nearly half the African-American vote. Still, the flap speaks to the needle he will have to thread throughout the primary campaign: maintaining his likeability and positivity in a political climate where nice guys finish last.

A big part of Biden's appeal is that he is a throwback to a time when politics were less mean and divisive. For many Democrats, that time is 2015, when Barack Obama was still in office (with Biden as his trusty veep) and before Donald Trump took his escalator ride to his own presidential announcement. But Biden obviously goes back a lot further than that, and the pace of social change inside today's Democratic Party is rapid.

Moreover, rank-and-file Democrats are angry. Where Biden likes to talk about his constructive working relationships with Republicans, many Democrats are outraged by Trump. Where Biden once supported a border fence to combat illegal immigration, many Democrats are incensed about the detention centers housing children near the border and the threatened deportation raids. Where Biden until recently supported a ban on most taxpayer funding of abortion, many progressive activists say "shout your abortion."

The question for Biden is how to get past these angry voters — who might find the former vice president's affability an ill fit for the current political moment — to the general election, where the civility pitch could be much more of an asset (and contrast with Trump). And he has to do all this while keeping policy position changes and apologies to a minimum, or else he will look like a weak flip-flopper.

One possibility is that the Democratic primary electorate is less angry than it may appear through the prism of the online left. That is probably especially true of Biden's coalition of white moderates, black voters, and senior citizens, who aren't always as vocal but are pretty reliable at the polls. Most of the other Democratic presidential candidates are going to compete for voters to Biden's left. Only South Bend, Indiana Mayor Pete Buttigieg seems to be seriously encroaching on Biden's turf.

Under this scenario, Biden could keep the least angry and woke Democratic voters to himself, winning pluralities and eventually majorities in a crowded field. The problem, however, is that he has such a large number of opponents who are going to be working overtime to draw contrasts with him. While that hasn't done much damage to him yet, there is no guarantee it won't begin to leave a mark as voters really start paying attention. In the debates, all the Democrats will have every incentive to swing at Biden early and often.

We have seen candidates start with leads as large as Biden's before. Usually the challengers can winnow that lead but not entirely eliminate it. This happened with Republicans Bob Dole in 1996 and Mitt Romney in 2012. Or the field itself could shrink and one main opponent will emerge, as when John McCain broke out against initially high-polling George W. Bush (McCain still lost).

Jeb Bush briefly led polls of national Republican voters in the 2016 campaign cycle. Like Biden, "Low Energy" Jeb was a nice guy out of step with his party's anger. The result was getting trounced by Trump. Trump used Bush as a foil in the debates. There's a risk some enterprising Democrat will figure out how to do the same to Biden.

Yet Biden is a much stronger frontrunner than Bush ever was, and there is no one who commands the amount of media attention that went to Trump. A more troubling precedent for Biden might be Rudy Giuliani, who sat atop the national polls for a year and then failed to win a single primary. Biden is unlikely to ignore the early voting states like Giuliani disastrously did. It is nevertheless an example of what can happen when a field of rivals spends months trying to drag the frontrunner down to their level.

Democrats may be skeptical that the best way to beat someone like Trump is by being as civil as possible. It's up to Biden to persuade them that everyone who has tried to play Trump at his own game has lost — while almost every other Democratic presidential candidate tries to convince them otherwise.