I’ll get a bit conspiratorial here, but if what Bernie has said is to be trusted in his video about oligarchy, up on his youtube channel, then Democrats are largely owned/influenced by billionaires who would benefit from the increased Trump support. It would make sense to do this, but yeah it could also just be a blunder, given how Trump was the first one to propose the ban and Democrats could take it as “hey if we do this, we’ll win the moderate right support again!!”, though who knows.