It is saying something like 'unlike all the other people, you can trust Nixon'. So the indefinite article is used because it It is referring to one name among many. It is intended to be ironic and humorous, because Nixon here is almost certainly referring to President Nixon, a president of the USA in the 1970's who resigned from office after being involved in a scandal and dishonesty (look up 'the Watergate Scandal')
Sorry, this was meant to be an answer, but I commented by mistake and cannot delete it