Gavin won't wash with conservatives, and shouldn't. The nation needs a unifier who can put himself/herself either above or to the side of the fray. A traditional leftist (especially a San Franciscan) isn't going to work. Were it George Moscone I'd agree.
You know who'd beat the snot outta Trump? Arnold the Terminator. Alas he's not US born. He's conservative in name but actually an apolitical country-lover first, like Reagan was. Or like Kennedy. IMO. That's all an open can of worms, yes.
I realize politically all were perceived as askew by those on the other side of the aisle, but all were thought of as men first (i.e. with personality, strength, charm, character) by the "average" American and as politicians second. That's what/who America needs. It can probably come from either party.
Note I am not especially liberal, nor conservative :). Just a pragmatist who recognized what Trump was instantly 25 years ago and thinks of him as nearly the very worst person in the country to have his job, second only to Charles Manson.