Unfortunately there is a double standard. It is particularly effective to accuse a conservative of being gay. If he denies it, he will be either called a liar or "homophobic." Some conservatives might turn against him (even if he has a good voting record).
Suppose he doesn't say anything one way or the other. The left will say how can we trust someone who can't answer a simple question about his private life. These are the very people who rush to the defense of a Ted Kennedy or a Bill Clinton -- again, double standards rule.
Suppose a conservative is accused of being gay and he admits to being gay? This will alienate some of his power-base, even if he has a good voting record. Meanwhile, the left will accuse him of not being gay enough -- if he were really "sincere" in his gayness, he would be a good little Marxist and not a Republican.
Finally, suppose a conservative is accused of being gay but there is ample evidence that he is not gay. Suppose he goes to the extent of producing ex-girlfriends and no one can find a, ugh, boyfriend or any evidence of strange encounters. First of all, there is something pathetic about a man having to give details about his personal life to try and prove he isn't gay. Also, the fringe leftists will have a field-day. If a former girlfriend is attractive, the militant lesbians will get indignant and accuse the man of "lookism" and find him guilty of all sorts of affronts to political-correctness. The only N.O.W.-approved heterosexual men are Ted Kennedy and Bill Clinton.
The double standard thrives in part because no one expects a leftist politician to follow the norms of conventional morality. A leftist can even preach about morality and he will be given a pass for anything short of being caught with a live boy or a dead girl. The way things are going, even this minimal standard is in doubt.