Grayson and DWS will lose. Both are too partisan and are only in congress because their districts were drawn specifically for them.
It's not as if Mr. Rubio is terribly unpopular, or scandal-ridden, or anything of the sort. Democrats need Murphy or Graham to win, and that's a fact. (Heck, I'd be willing to vote for either one, as they're both in the more conservative side of the democratic party, and Rubio's hardly some moderate stalwart and is willing to flip-flop solely for political gain.)
Grayson's district was actually drawn as a Puerto Rican opportunity district. Whenever he retires he will probably be replaced by a Puerto Rican Democrat.
Love Grayson, not a DWS fan, but neither should run. Murphy would be the best for the Dems.
