When you demand the President show his long-form birth certificate, and his college grades, while at the same time refusing to release your tax records, you are a racist, a hypocrite, and totally unfit to be a public servant.
Leftist 101: If you don't agree with us, you're racist/sexist/homophobic. If you support someone else who doesn't agree with us, you're racist/sexist/homophobic by association.
That's usually what the first line of argument from the left boils down to. Not always, but certainly more often than not.