I call to memory the recent election of Danica Roem down in Prince William County, VA. (First openly transgender elected to the VA House of Delegates) There was a HUGE amount of money from outside VA that poured into that local election.
If Manning is able to mobilize even a portion of the same groups (after all, the label "transphobic" is a positive one among leftists) then there could be a real race. I have no doubt that Cardin will win in the end, but it could be bloody.
My prediction is that the huge amount of money will go to the incumbent, and he will coast to an easy victory without spending hardly anything. Remember that Manning is facing him in a primary—not a general election.
The situation might draw some LGBT votes away from the incumbent, but it won’t make a difference, especially in a primary.
And don't think this hasn't registered with the major factions in the Democratic Party.
Manning may be an unstable freak and convicted felon, but he will have backers with money and campaign experience, and enough of a base of hard-left anti-American nihilists to make the primary race interesting.
And what if, by some miracle, Manning wins the primary? Does Maryland have a "sore loser law" that would prevent Cardin from running as an independent?
Does the GOP have candidates willing and capable of being other than the usual sacrifical lambs in Maryland?
It would not be wise to underestimate Manning--not the man, but those who would use him. He might be wholly unsuitable to serve, but not wholly incapable of being elected.