There may be some truth in that. I think until people feel it is accepted to openly disapprove, they may be inflating his numbers. Much of this will also be based on your community. I told my wife there is no way we are going to put a negative Obama sticker on our car, because where we live, our car would be set on fire if we ever left it unattended.
Get a “Dissent is the highest form of patriotism” bumper sticker. It’ll take the liberals a while to figure out that you are anti-Obama.