After two years of speculation about which of them is best suited to bring the Trump era to a merciful end in 2020, Democratic politicians who have been spending their free time forming exploratory committees, soliciting donations, giving inspiring speeches, and hanging out in Iowa diners are at last announcing formal bids to become the next president of the United States. Over the next few weeks, we'll take a look at each of the front-runners: Who are they? What do they stand for? And in order to have a shot at winning the nomination they seek, what tough questions will they have to answer first? Previously, we looked at Kamala Harris. Up next: Vermont senator Bernie Sanders, who is expected to announce his presidential bid any day now.

1. Can he convince voters he isn’t stale?

Bernie wasn’t supposed to win a damn thing back in May 2015, when he launched a long-shot campaign in a primary that was supposed to be an extended coronation for Hillary Clinton. As it turns out, however, in one of the most unequal developed countries on earth, there was a real appetite for an unabashed democratic socialist who promised a political and economic revolution, and Sanders ended up winning 46 percent of pledged delegates before conceding to Clinton at the Democratic National Convention.

Becoming a major-party nominee after one almost becomes a major-party nominee is not unheard of: Mitt Romney, John McCain, and Hillary Clinton each won the nod after finishing as first runner-up in their party’s previous contested primary. But candidate fatigue is a real thing, and you will note that those three have something else in common, too. Some of the tepid support Clinton received from some Democrats can be attributed to the fact that they were asked, in effect, to get excited about a candidate whose spiel they had literally heard before—and on whom they had decided to pass.

Maybe Sanders wouldn’t suffer the same fate; unlike the more moderate pitches made by Romney, McCain, and Clinton, his platform is very much on the rise within the party. But he won’t be the only prospective progressive candidate in 2020, which means he’ll have to work to earn some of the supporters that, last time, went to him by default. Look for him to focus heavily on his longtime advocacy for Medicare for All, in an effort to differentiate himself from the Johnny-come-lately Democrats who have only embraced single-payer health care since it became a mainstream position.

2. Can he and the Democratic Party make peace with one another?

Although Sanders sought the Democatic nomination in 2016, the thrice-elected senator is not and has never been a Democrat—a fact his detractors are fond of pointing out. (An independent who caucuses with the Democrats, he joined up in 2016 to participate in the primaries, and un-enrolled after the race was over.) It is the source of much of the residual bitterness about Sanders among the party establishment: He availed himself of all the privileges of membership, the argument goes, but accepted none of the responsibility. And even today, he still won’t call himself one of them.

On the one hand, this maneuver makes sense: Running as a Democrat is what gets him on the debate stage, and allows him to influence the proverbial Conversation. And he surely knows that the presence of a true independent on the ballot would all but deliver the election to the Republican nominee. On the other hand, some of Sanders’ devil-may-care choices since becoming a celebrity—his unapologetic endorsement of an anti-choice Democratic mayoral candidate in Nebraska, for example—have rankled members of a party still trying to figure out if and how he fits in to its future.