Moulton better win. The choice is so clear: lose the seat, or keep it easily.
Yeah, the only thing that's scaring me away from Moulton is that he's not progressive enough for me. On one hand he's not nearly to the left as Tierney is, but on the other he's (obviously) better than Tisei.
I'm all for supporting the most progressive candidate, but when there's an electability gap as massive as this, it's an easy choice. It's not like Moulton wouldn't be a reliably Democratic vote anyway (and certainly, like you said, much better than Tisei).