Las Vegas sports books aren’t allowed to make lines (except for fun) on who will win the presidency, but betting on elections is popular in online books.
Barack Obama has been favored over John McCain from the point of their presumptive nominations, and he’s currently about a 9-5 (-180) favorite. Because the bookmaker has to work in his edge, you wager more or win less than this number on either side of the proposition, which works out to being able to bet roughly $200 to win $100 on Obama, or $100 to win $160 on McCain.
These odds have changed quite a bit from the opening. Looking only at a wager on the underdog, by betting early you could have gotten as much as +220 on McCain (better than 2-1). But over several weeks, the odds came down to the point where you could get only +145.
Immediately after the Democratic convention, however, the same "bounce" that raises the convention-sponsoring party’s status in the polls also affected the odds, and the price on McCain went back up to +165. You can expect the same effect to lower the odds on McCain immediately after the Republican convention, so basic strategy indicates that you should wait until after the convention concludes if you want to bet Obama (because the lay price on him will correspondingly drop).
From that point, market forces will take over to move the line up until election day. By the way, the line on a third-party winner is currently about 60-1.
