There are also a lot of fairly conservative Democrats in the south, in particular, that are strongly pro-gun. He can’t risk alienating them just yet if he wants to win in the fall.
That’s also why you see a few Democratic senators taking a more conservative line on the 2nd amendment. They know that if they want to keep their job, that’s one issue that they can’t cross the line on.
It certainly didn’t help spotted-owl gore.