To me it means someone who gets screwed over and doesn't have the stones to stand up for himself, like a guy whose wife cheats on him and because he doesn't have the spine to leave her, he just takes it. Like Bernie Sanders did when Hillary and the DNC, including Donna Brazille stabbed him in the back and threw him out with the trash and instead of fighting back, he got in line and endorsed the most crooked politician of all time.
You can go ahead and spend 2 pages arguing about the meaning of the word and whether or not it's appropriate to avoid the subject, but the reality is, the old loon bag isn't what he's held out to be. He's just another opportunistic lap dog, who also happens to be out of his mind and a moron.