Donald Trump has being doing his best to lob the “birther” grenade back into American politics – just as Mitt Romney is trying to get his campaign on track. He told CNBC on Tuesday (see below) that the mainstream liberal media were not looking more closely at fresh claims that Obama was not born in the US. He helpfully added: “I’ve been known as a very smart guy for a long time.”

In an interview with Wolf Blitzer on CNN a couple of hours ago, Trump asserted that this is “not an issue that he [Obama] talking about, so he uses reverse psychology on people like you.”

Blitzer: I don’t understand why you’re doubling down on this birther issue after the state of Hawaii formally says … ‘this is official, he was born in Hawaii’ … Why do you deny that?

Trump: A lot people do not think it was authentic. His mother was not in the hospital, there are many other things that came out. And frankly I think if you would report it accurately, I think you’d probably get better ratings than you’re getting, which are pretty small.

The two men talk across each other for some time, and then …

Blitzer: Donald, Donald. You’re beggining to sound a little ridiculous, I have to tell you.

Trump: No, I think you are, Wolf. And let me tell you something. I think you sound ridiculous.

As Richard Adams puts it in his Guardian liveblog, “At any moment it seemed like Trump was going to say, ‘I know you are, but what am I?’”