Biden is or will be the Democratic nominee. With 1677 delegates still to be awarded, Biden need 775 of them to reach the magic number of 1991. That 46.2% of all delegates left. Sanders needs 1077 or 64.3% of the remaining delegates. In simple English, Sanders must defeat Biden by 30 points in all remaining primaries to get the nomination. That isn't about to happen as Biden has leads of 10 to 30 plus points in the remaining states that have been polled.

The primaries scheduled for 4 Apr, Wyoming, Alaska and Hawaii, those states haven't been polls.

Wisconsin on 7 Apr has Biden up by 9

Primaries on 28 Apr
Pennsylvania Biden by 23
New York Biden by 16
Rhode Island hasn't been polled
Delaware Biden by 22

May and June primaries are too far out for a poll to be meaningful.

Now why would some Sanders supporters support Biden? They didn't support Hillary in 2016. We don't know how many stayed home as exit polls can't poll them. But we do know that Democrats voted for Hillary by a 89-8 margin over Trump with 3% voting third party. Sanders supporters who showed up at the polls did vote for Hillary, but by a 75-12 margin with a whopping 13% voting third party. Recent estimate place the percentage at 25% of Sanders supporters that won't vote for Biden. That's good news if one is a Trumper.

It's high past time that we start electing Americans to congress and the presidency who put America first instead of their political party. For way too long we have been electing Republicans and Democrats who happen to be Americans instead of Americans who happen to be Republicans and Democrats.