Political futures markets

I watch two markets that trade “political futures,” i.e., contracts whose values depend on the outcome of political events. (These markets trade other futures as well, but for the moment I am interested in the U.S. presidential election.)

TradeSports has W. currently at about 67.6, whereas the Iowa Electronic Markets has W. at 72.5. For a while the contracts on W. traded lower at TradeSports than IEM, but now it has reversed. In either case, there is an opportunity for arbitraging. But I suppose these markets are not big and efficient enough for people to bother doing this.