Donald Trump has said he would be “open” to accepting a Cabinet post if Mitt Romney becomes president. Trump would prefer “a position where I negotiate against some of these countries, because they are really taking our lunch.” So is he on the short list, perhaps, for secretary of state?

Don’t laugh. OK, go ahead and laugh. Point out that Trump is barely qualified to be secretary of salami.

But then ask Romney why he chooses to embrace and encourage a puffed-up buffoon whose antic self-promotion, once mildly amusing, has become rabid and toxic. Ask Romney if giving Trump a platform doesn’t cheapen what should be a serious debate about the future of the country. Ask Romney why he decided to join a huckster’s silly sideshow.

In a week when Romney clinched the Republican nomination, his appearance at a Las Vegas fundraiser with Trump — and Trump’s doubled-down insistence that the thoroughly discredited, insane “birther” theories about President Obama have merit — dominated the political news.

When pressed by reporters on Monday why he continues to associate with Trump, Romney gave an answer that was unintentionally revealing. “You know, I don’t agree with all the people who support me, and my guess is they don’t all agree with everything I believe in,” he said. “But I need to get 50.1 percent or more, and I’m appreciative to have the help of a lot of good people.”

This raises two issues, the lesser of which is the suggestion that Romney will accept endorsements and donations from anyone who chooses to give them. One hopes that when he was running Bain Capital, he took his obligation to perform due diligence more seriously.

The greater issue is this: Romney thinks Trump actually has the Romney campaign’s best interests in mind? Really? If so, one has to wonder if Romney is too gullible to be president.

The idea that Trump cares about anything bigger than Trump is absurd. In his mind, from all evidence, there is nothing bigger than Trump.

If he really wanted Romney to win, he wouldn’t have done an interview with CNN’s Wolf Blitzer that deserves a prominent place in the annals of lunacy. Trump begins by slamming a taped introduction as “totally inappropriate” and “actually very dishonest” because it focused on the birther nonsense. He goes on to tell Blitzer that Obama “uses reverse psychology” and pretends nonchalance about discussions of his origins when actually “it’s not an issue that he likes talking about.”

I should interject that back here on Planet Earth, the Obama campaign did all it could this week to focus attention on Trump and birtherism. The mood of top advisers seemed to approach unrestrained glee.

Poor Blitzer notes that Hawaii has formally certified Obama’s birth certificate. Trump contends that “many people” do not believe the document is authentic.

“Like who?” Blitzer asks.

 “There are many people,” said Trump.

“Give me a name of somebody,” demands Blitzer.

“There are many people,” said Trump. “I don’t give names.”

Indeed, Trump refuses to violate the Super-Secret Birther Code of Silence by naming a single person who doubts the facts of Obama’s birth. He does pin himself down, however, when Blitzer asks whether “the conspiracy” is supposed to have begun in 1961, when announcements of Obama’s birth were published in two Honolulu newspapers.

“That’s right,” Trump said. “And many people put those announcements in because they wanted to get the benefit of being so-called born in this country. Many people did it. It was something that was done by many people, even if they weren’t born in the country. You know it, and so do I, and so do a lot of your viewers.”

This is transparently crazy — and also stupid. It is a bald-faced lie that “many people” — or any people, far as I can tell — ever published fake birth announcements in hopes of establishing citizenship. Moreover, Obama has to be a U.S. citizen, even if he were born on the moon, because of his mother’s citizenship. Trump needs to hire some writers to come up with better material.

As for Romney, he needs to decide whether Trump is the sort of person on whom he wants to rely for support and advice — if he’s one of the “good people” Romney would be proud to have at his side if he becomes president.

Oh, sorry. Looks as if that choice has already been made.

Eugene Robinson is a Pulitzer Prize winning columnist and writes for The Washington Post. He can be reached at eugenerobinson@washpost.com.