It's obvious that Donald Trump's recent bout of Birtherism is primarily about garnering Trump some free pub -- but considering how readily they're airing it at Fox News, it's starting to look like a combination of Swift Boat/Clinton-scandals type of Republican tactics, where just having the smears "out there" helps keep their targets' negatives high.

It's also obvious, after Trump's appearance last night on Bill O'Reilly's Fox News show, that he really isn't a serious candidate. Instead, Trump is being a stalking horse who can make the rest of the Republican field look sane and serious by comparison.

Consider this exchange:

O'REILLY: Now, when you were on "The View" and they didn't walk out, which they should have because they walked out on me and they should have stayed. You were way, way worse than I was on "The View." You were hammering the birth certificate.

Now, we very early on did an investigation about Barack Obama's birth certificate. What "The Factor" found out was there were two announcements the week he was born in both Honolulu newspapers saying that he was born, OK. That is impossible -- that is impossible to make happen if he had not been born in the hospital. So therefore, I just put it to bed. I said he was born in Honolulu. The two newspapers documented it. His mother was a hippy. His father was a guy from Kenya who split. There couldn't have been a sophisticated -- what is he, Baby Jesus? -- there was a sophisticated conspiracy to smuggle this baby back into the country? So I just dismissed it. But you made a big deal of it.

TRUMP: Bill, I grew up with Wall Street geniuses. What they do in terms of fraud and how they change documents and I will tell you something. If you notice those dates were three days later. Here is what I ask people. Who puts announcements? Here are two poor people, a man and a woman with no money, they have a baby. There's announcements in the newspaper?

O'REILLY: The grandparents did it.

TRUMP: Excuse me. The grandparents. Nelson Rockefeller doesn't put announcements.

O'REILLY: Sure, there are birth announcements all the time.

TRUMP: I have never seen one.

O'REILLY: Really? They are common.

TRUMP: I've never seen one.

O'REILLY: But why is this important to you?

TRUMP: Because if you are going to be president of the United States you have to be born in this country. And there is a doubt as to whether or not he was born…

O'REILLY: Oh come on. Do you really feel this about him?

TRUMP: You know, I started off by saying -- and I always do and I did on the "The View." I'm a very smart guy. I went to the best college. I had good marks. I was a very smart guy, good student and all that stuff. Because what they do to the birthers, which is a term I hate because a lot of these birthers are just really quality people that just want the truth. What they do to the birthers is unbelievable to a point where people are afraid to talk about this subject. They are afraid to confront you or anybody about this subject.

O'REILLY: Do you think it's an important subject?

TRUMP: Listen, I have a birth certificate. I have my birth certificate. And in fact, they said the one I gave yesterday wasn't good enough. So I actually got the one from the Health Department, which is the perfect one. Because they were saying the one I gave yesterday wasn't good enough, so I got the other. People have birth certificates. He doesn't have a birth certificate. He may have one but there's something on that, maybe religion, maybe it says he is a Muslim. I don't know. Maybe he doesn't want that. Or he may not have one. But I will tell you this. If he wasn't born in this country, it's one of the great scams of all time.

O'REILLY: Absolutely. But I don't think that's the case.

TRUMP: You don't, but I'm starting to think.

O'REILLY: I don't think you believe that either. I think it's provocative, you get a lot of attention raising the question. But I don't think you believe it either.

TRUMP: Two weeks ago I felt like probably he was born in the country. Today it's possibly. I'm telling you it's changed. I have seen too many things.