Because Biden is casting a shadow that extends beyond his own candidacy. Sens. Cory Booker of New Jersey and Kamala Harris of California, as well as former Housing Secretary Julian Castro, might still be in the race had Biden not been a presumptive favorite among black and brown voters. It becomes critically important to determine sooner rather than later who would get that support if Biden were not a factor.

Then there’s the matter of clogging the center lane. Those of us who believe that the Bernie Sanders wing of the party is not the best bet in this election are concerned about finding the strongest alternative — a progressive with some level-headed flexibility. Former South Bend, Indiana Mayor Pete Buttigieg and Minnesota Sen. Amy Klobuchar made good showings in New Hampshire. They and former New York City Mayor Mike Bloomberg, are jockeying for centrist support. Biden, as long as he stays in, is in the way.

Biden backers I spoke with across Iowa lacked enthusiasm. Their support for the dignified former vice president was almost perfunctory, as if Biden was the safe, default candidate to topple Trump. This election demands more.