The Democrats are really good at it.
They target Republicans early on for the strategy of crazy which was successful against the Tea party movement, a consistent blogosphere and media attempt to create a deadly public perception of a rising Republican star.
We’ve seen this already in The “crazy-ing” of Marco Rubio, an effort which continues via Lawrence “The Fighter” O’Donnell and others.
I see they’re doing it already to Rand Paul, as reported by Ann Althouse (h/t Instapundit):

“GOP Senator Pushes Gun-Running Conspiracy Theory During Benghazi Hearing.”

That’s the way they put it over at Think Progress. I’ve watched the video. Rand Paul asks a question. It seems histrionic to equate asking a question with pushing a conspiracy theory, and the truth is Hillary Clinton’s answer has the ring of… lying.
The effort on the left to stereotype Rand Paul as a nutcase is so strenuous that it stimulates my root-for-the-underdog instinct. And makes me suspicious. I feel a Rand-Paul-must-be-destroyed conspiracy theory blossoming within.
The goal of Think Progress is that in a year or so Rand Paul, Paul Ryan, Marco Rubio, and Bobby Jindal, among others, will have high negatives and be labeled in the public mind as “extremist” crazy people.
We need to counter this effort to kill our candidacies in the cradle, and to focus on doing the same.