Is there a Democrat who could successfully primary him/force him to retire?
Middletown Mayor Dan Drew has already entered the race, and I'm sure a lot of Democrats don't want Malloy to be the nominee. Malloy would probably win the primary if he runs, but I don't think he's going to run again.
Did he? My mom's cousin is very involved in Middletown politics and campaigned for Drew's opponent last election despite being a staunch Democrat, supposedly because Drew used his position in the Middletown DP to keep a dissenting Democratic council member off the ballot. He's also very close to Malloy, as he campaigned in Middletown for him because the election was expected to be close, even though it wasn't. I'd be shocked if he challenged Malloy.