After the events of the past week, the one-on-one competition between Biden and Sanders is just beginning but already the calendar says their battle is at an advanced and potentially decisive stage. Assumptions that Democrats are headed toward a genuinely contested convention might well be wrong.
Sanders has been here before. Four years ago, the senator from Vermont lost South Carolina to Hillary Clinton, lost the majority of states on Super Tuesday and fell behind in the delegate race. But he won in enough places on Super Tuesday to give him the incentive to keep going - and he had a plan for regaining momentum in Michigan that included early television ads and a focus on trade in a state sensitive to the issue.
The pre-primary polls showed Clinton with a substantial lead, but on primary night, Sanders won. The margin was narrow - less than two percentage points - but the value of the upset was enormous. The victory revived his campaign, and he took his fight all the way to the convention in Philadelphia, to the dismay of Clinton forces.
That history makes Michigan the most crucial of the six states with contests this Tuesday, but Sanders could struggle to repeat his performance of four years ago. He won't be able to sneak up on Biden as he did with Clinton.
Biden has done well with some of the kinds of Michigan voters Sanders relied on for success in 2016, whether those in small towns and rural areas or those without college degrees. Sanders still has strength in areas with colleges and universities, but by his own acknowledgment, he is not getting the turnout from young voters that he needs. Meanwhile in Michigan districts with large concentrations of African Americans, Sanders lost big in 2016, and Biden has been winning black voters by huge margins this year.
Sanders has other potential problems Tuesday. Three of the six states with contests held caucuses four years ago; Sanders got 78 percent of the vote in Idaho, 73 percent in Washington and 64 percent in North Dakota. He netted 68 delegates in those three contests. This year Washington and Idaho have shifted to primaries. Even if he wins all three again, and polling in Washington shows a close race, Sanders won't get nearly as many delegates.
Overall, between now and April 7, Sanders and Biden will compete in 17 states. Four years ago, Clinton won nine of 17 and Sanders won eight, six of them caucuses. Of the 11 that were primaries, Clinton lost only Michigan and Wisconsin. From those 17 states, she emerged from with about 100 more delegates than Sanders.
Those numbers set the stage for what is about to unfold in the Democratic campaign, with the prospect that Sanders could come out of the contests between now and the Wisconsin primary farther behind Biden in delegates and with no realistic path to make up the difference.
Sanders faces a big defeat Tuesday in Mississippi, a replication of 2016. He was competitive with Clinton in Missouri, but this year he has to break Biden's momentum to avoid losing ground there. The following week, he can expect a big loss in Florida: Four years ago, Clinton beat him by a margin of 30 points. His praise for Fidel Castro's literacy program adds to his problems there this year.
A week after that, on March 24, there is a stand-alone primary in Georgia. Clinton crushed Sanders there in 2016, winning more than twice as many delegates. Because there is no other event that day, a big Biden victory will feed a story line of the former vice president's strength among the party's most loyal constituency. Five days later, there will be the Puerto Rico primary, which Sanders lost against Clinton.
On April 4, Sanders can look forward to some relief. Four states have contests that Saturday, and three of them will be caucuses, with Louisiana holding a primary. But the four have only 107 pledged delegates at stake, hardly enough to change things significantly.
The one potential bright spot for Sanders comes on April 7 in Wisconsin. Four years ago, he won the Badger State by double digits. A loss in Wisconsin this year would be a huge setback. But even a victory of near-double digits would almost certainly still leave Sanders behind Biden in delegates. After Wisconsin, Sanders will be looking at primaries in several states that don't allow independents - generally a Sanders constituency - to vote.
As this indicates, almost any back-of-the envelope calculation of a two-person race gives Biden the advantage today. The latest model from Nate Silver's fivethirtyeight.com says Sanders has only a "small window" to win the nomination, while Biden has an 88 percent chance of winning a majority of pledged delegates and a 94 percent chance of winning a plurality.
As Silver put it, "Sanders has to come back quickly when the momentum is currently against him in a bunch of states that are not very good for him - or it will be too late. It's not impossible. But the chances are low."
Sanders has said that whoever has the most delegates, even if it is just a plurality, should become the nominee. When he first said that, he was confident that he would be the person with a plurality by the time the primaries end. That statement could come back on him sooner than he thinks, possibly in the days after April 8.
No one anticipated that the Democratic race would turn as quickly as it did. No one figured that Biden would sweep as many states on Super Tuesday and grab a narrow lead in delegates. No one assumed the field would consolidate so quickly and decisively around Biden. Biden could stumble badly in the March 15 debate in Arizona or do something else to give supporters pause.
Realistically, however, it is Sanders who has potential soul-searching ahead. Four years ago, he resisted calls to endorse Clinton immediately after she won the June primary in California. He took his campaign into the convention hall in Philadelphia and pressed his demands on the Clinton campaign. For Clinton, it was an annoyance, but no one assumed it would be costly in the general election.
This year, Democrats will need every day possible to prepare for the general election against President Trump. The Trump reelection campaign has been running its general election operation for many months, raising huge amounts of money, building organizations in states, modeling the electorate and most important communicating with the voters they believe will determine the outcome of the election.
Early this year, David Plouffe, who was Barack Obama's 2008 campaign manager and a guiding hand from the White House in the president's 2012 reelect, said he believes Democrats must effectively wrap up their nomination contest this spring, rather than early summer, to avoid putting their general election chances at risk.
By early April, Democrats should know definitively whether Biden will be their nominee or whether Sanders still has a chance of winning. If Sanders does not have a chance of winning, will he take his candidacy all the way to Democratic convention again or choose a different path than he did in 2016?