The poll, which was conducted from July 7 to July 9, found that 73 percent of Democratic voters “somewhat” or “strongly” approve of Harris as Biden’s replacement. In an earlier iteration of the same survey, conducted from July 3 to July 6, a 66 percent majority of Democrats approved of Harris as a replacement.
If they try to change Biden at this point, republican states will invalidate the Democrats for failing to have their nominee by the deadline.
It doesn’t matter if it would be tossed out on legal challenge previously, the SCOTUS will invent a reason to uphold it. Trump wins.
Biden is the candidate. Let him run. Make him win. He can step down and hand it off to Harris later if he needs to. But the process is too far along now to go with another.