To their detriment? I'm not sure. They just had the Republican convention. At that convention, they took a lot of shots at Biden. Now the Democrats say "Wrong target, suckers!"

They take over the news cycle from the Republican convention, and they neutralize a huge amount of the talking points from the convention. That could be pretty brilliant.

(I mean, it would have been better for Biden to clearly not be running last year at this time, and let the primary process do its thing. But dropping out right now might be pretty decent timing.)