This has been a remarkable fortnight. Between February 29 and March 10, Democratic elites and voters shifted from a large, fluid field toward a frontrunner who appears destined to win the nomination. Joe Biden has emerged as the consensus candidate as he surged ahead in national polling, high profile endorsements, and the delegate count.

Bernie Sanders, once again, finds himself trapped in a respectable second place. The delegate math is working against him. The Democrats have zero “winner-take-all” primaries, so recovering from a deficit requires large victories in a string of delegate-rich states. Michigan (125), Washington (89), Missouri (68), Mississippi (36), Idaho (20), and North Dakota (14) vote today, while Florida (219), Illinois (155), Ohio (136), and Arizona (67) vote next Tuesday. The next major bloc of delegates comes April 28 when New York (274), Pennsylvania (186), Maryland (96), Connecticut (60), Rhode Island (26), and Delaware (21) cast ballots. Based on reasonable projections, Biden is favored in all these states except Washington and Rhode Island.

Sanders needs a shift in the contest’s political dynamics. What are the most likely possibilities? Bernie could expand his coalition to eat into Biden’s natural constituencies. This seems unlikely. Sanders has missed his chance to appeal to other elements of the party. He has maintained his insurgency strategy, positioning himself as an outsider seeking to redefine the party. To win, this approach would have to overwhelm the party with new voters or convert current partisans to the cause. Neither has happened.

An alternative could be a dramatic event, external to the campaign, that reconfigures reality. The Coronavirus, and the possible economic consequences connected to it, could shake up a campaign, but it is difficult to see how it would benefit Sanders alone. If voters turn on President Trump because of the government’s handling of the virus, Democrats would gain. If Biden is still seen as the most electable candidate, he stands to profit the most. An exception could be if elites, as a class, are held responsible, thereby empowering Sanders’ appeals for transformation, but blame would have to spread across the political and economic spectrum for this to happen.

What Sanders needs is an event that damages Biden, strengthens Sanders, or both. Biden’s health is the most obvious possibility. He appears to be frail on the stump, struggling to string together coherent answers or thoughts. If today goes well for Biden, his campaign will probably start to limit media access and reduce his public speaking schedule. If Biden’s health worsens, or if medical reports confirm a problem, the race still has time to change again.

This highlights what has not changed over the past two weeks. Joe Biden held a firm lead for the nomination up until the debate schedule began to heat up and voters started to tune into the contest. Biden suffered in comparison to his rivals. The idea of Joe Biden was better than actual Joe Biden. What hobbled him during the grind of the process will hamper him over the next few weeks and months. While the party may be consolidating behind him, this alone will not transform Biden into something better.