>I actually wonder if leftist radicals are even numerous enough
>to really make a difference.

they aren't numerous enough to make a difference.
you have diagnosed this correctly:

>Are you sure they are the
>problem, and not a larger mass of politically disinterested
>voters that don't feel addressed by democrats or trumpists?
>What are dems doing to reach them?

nothing.
even though that's why OBAMA, the last Democratic Party president won.
All they have to do is copy the SUBSTANCE of the Obama campaign and win. All they seem to do is copy the artifice (see Buttigieg, Harris).

the "left" isn't the problem.
nor are the third party voters.

it's the lack of attention toward EXPANDING the vote, and trying to impose things from the top down. The "Boss" mentality.