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1. The expectation was for a long, drawn-out primary with many candidates. But more quickly than anyone expected, the Democratic primary has come down to Bernie Sanders and Joe Biden.

2. Joe Biden was all but counted out before last week. A crucial endorsement from Congressman James Clyburn helped him cruise to a resounding victory in South Carolina. After his moderate rivals Amy Klobuchar and Pete Buttigieg dropped out to back him on the eve of Super Tuesday, he came roaring back.

3. And the Democratic establishment –  I’m talking about the Democratic National Committee, the major Democratic funders and bundlers, the platoons of political consultants and advisers, pundits and op-ed writers, and corporate media – suddenly came down like a ton of bricks on Bernie Sanders and rallied around Joe Biden to help give Biden decisive victories in key states.

Neither Biden nor Bernie is a perfect candidate. Bernie’s personality grates on some, while Biden’s policy history turns off some. In the coming contest between Bernie and Biden, younger and older Democrats have very different ideas about who can best defeat Trump. The generation gap is huge. The biggest problem with Biden’s electability is he is practically incapable of connecting with young people. In Massachusetts on Tuesday, Biden won just 18 percent of voters under 45; in Texas, just 16 percent of voters under 45; in Minnesota, just 17 percent; in California, an appalling 8 percent. Sanders does almost as poorly among voters over 65.

The eventual nominee will have to bridge the divide between these factions within the party. Bernie must find a way to tailor his populist message in a way that will appeal to older voters, and black voters in particular. Even with strong policies on racial justice and equality, Bernie’s message still has not resonated with black voters. If he wants to be the nominee, something must change.

And the only way Biden can win the presidency is if he reaches out to young, progressive Democrats, and inspires them. This poses a huge lift: Biden’s establishment message of maintaining the status quo is as uninspiring as it gets for young voters who have only ever experienced the worst of our politics and the economy. In 2016, the Democrats’ presidential nominee had a similar message and similar problems with young voters. We cannot afford a repeat of a centrist candidate who stands for more of the same.

Perhaps Trump is so loathsome that whoever emerges as the Democratic candidate will attract enough votes to consign Trump to the trash bin of history regardless of their limitations. But we would be foolish to count on that.