Bet on Obama to win re-election. It's simple - Santorum is totally unelectable; and Romney is so weak and lacking the popular touch that he is getting owned by a guy whose name has been successfully turned into slang for the frothy mix of lube & fecal matter resulting from anal sex. This is the easiet can't lose bet I have ever seen in my life.
Santorum has nothing against anal sex. He just wants to stop minorities from breeding Republicans out of existence (his deisre to ban contraceptives)
Obama is quoted at around a 60% chance to win on Intrade at the moment. So a bet/trade for him to win would only net a 40% return.
A bet on Obama will get 40 units profit for every 60 units risked. Return is profit/capital employed. Since 60 units is the maximum you can lose on an Obama bet at the moment, you only need to put up 60 units not 100. And 40/60 is around 66%.
What if there is? Romney can't even win over Republicans - this shows he lacks the political charisma needed to be president. Santorum is just as unelectable as he ever was. Only thing to stop Obama is if he dies before the election.
I was including transactions costs - bid/offer spread, poor liquidity in the market etc. Besides, if you make 66% who cares what comes after the decimal point.