If the bookies are doing their jobs right, they'll make money either way. They set up the market, and the people who think Trump's odds are better than 20 percent will pay 20c for the shot at winning a bit less than a dollar, the bookie shouldn't let them buy it unless there's also someone who thinks $0.80 to win a bit less than a dollar sounds good. The bookie then holds onto the full dollar they get, and then pay out (say) 97 cents on {inauguration, electoral college vote, whatever}.