I can’t speak for others, but speaking for myself, I’m more likely to be convinced by someone who concedes a point here and there, and doesn’t pretend that what (or the person) he’s defending is right in all respects — in a real war, for instance, who admits that our side occasionally commits atrocities too (but doesn’t dwell on them — I agree about that), and counters that we don’t commit nearly as many as the enemy (and that a victory by us would be much more beneficial — or less harmful — than a victory by them). I don’t find praise or condemnation, if done in a simplistic way, to be convincing.
A 30-second radio or tv ad needs to be simple, of course. There’s no time for nuances. On an internet forum, though, there’s room for a bit more subtlety.
Levin endlessly trashed Trump long after he’d secured the nomination, providing implicit support to Hillary Clinton until weeks before the election when, in a transparent attempt to be able to claim to his audience that he fought against Hillary Clinton when he never had, he went through the motions of support but only with caveats about how he’d hold Trump’s feet to the fire etc etc followed by more criticisms.