Assad is the lesser evil compared to ISIS
He's still, y'know, evil.
He's a horrible person, no doubt, but I'd rather have him run things than ISIS.
But Gabbard hasn't simply said he's better than ISIS. She's gone on a trip to Syria in which she (apparently) only visited Assad-controlled territory, and talked to Assad-approved Syrians, then came back to the US, seemingly believing everything they said. No acknowledgement in her commentary of Assad's crimes, or that Assad might be manipulating the stories she was hearing on this trip.