The problem is that the guy would be a third party candidate, which means he would get treated as a sinkhole for the voters of the opposite party. This would work specially well for the GQP since they could just have a candidate adopt his ideology, throw a lot of money into news, media, and rallies to trump up support, and then easily turn around and just not fulfill it when they win. Meanwhile, there will be plenty of people in the other side of the flawed bipartisan system who will just blame democrats for not choosing their third party candidate regardless of the actual consequences voting third party has in USA’s democratic facade of a system.