What kind of backwards ass logic is that?
"Harris might do what I want, but to punish her for not doing it aggressively enough I'm going to make sure the guy who won't ever do what I want gets elected."
That doesn't sound like a hail Mary, that sounds like the tantrum of a petulant toddler who didn't get enough sprinkles on their ice cream so they decided to a pile dog shit instead.
Supporting person B doesn't pressure person A, it just tells person B that you support them.