Humor is very very risky, particularly for a candidate, unless he's been in so long that it just doesn't matter, and he's not running for president. But it's just that people are so sensitive and so touchy, and you're just going to upset somebody without ever realizing it.

This quote is explaining that using humor in a political campaign for a candidate can be dangerous because people are easily offended. It is especially risky if the candidate is running for president, because if they say something that offends someone there will be a strong reaction. The quote suggests that humor should not be a part of the campaign, because it is too difficult to predict how people will react.