Yes, this man could still be elected, if he is a great speaker and can get his points across in a way that will make him still liked. Hitler convinced his citizens to wipe out a race of people, just because he was a very powerful speaker they could believe in.
Someone who is staunchly against the currently accepted idea of how HIV and AIDS works would never manage to get elected in any major election. Most people are very aware of and accepting of how these diseases work, so a denialist would be looked down on and rejected offhand as less intelligent.
The United States voters have already shown they consider conservative views to largely be outdated, so even without being in a lunatic fringe group of truthers, a political conservative has the deck stacked against them. When you add this kind of nonsense to the mix they'd have no chance, like-minded people would vote for them but there aren't many of those. It would be a blowout.
For the vast majority of Americans AIDS is real and undeniable, therefore I believe it would be extremely difficult for a politically conservative AIDS denialist to be elected. This is somewhat two fold because the first problem would be denying AIDS, which many people would feel shows the stupidity of the politician. Secondly, America in general is no longer leaning towards the conservative side on most political topics, so that would make it even more difficult for the politician.
A politically conservative AIDS denialist would be laughed off the ballot as someone who is grossly out of touch with American values. AIDS has been a problem for more than 30 years with millions of deaths worldwide. Too many high-profile people have died of AIDS-related complications to merit a denialist getting elected to any office in the United States. If an AIDS denialist is elected, the American populace is truly sick and twisted.