Trump endorses Romney in 2012. (Ethan Miller/Getty Images)

There was an elephant in the room as Mitt Romney bashed Donald Trump in his speech on Thursday. (Yes, yes, lots of elephants — which is to say, Republicans. Very good!) How, one might wonder, was Romney hammering Trump when four years ago he stood next to Trump in Vegas and demurely received Trump's endorsement?

Romney explained on Twitter.

There you go. Romney had no idea that Trump was the type who'd shoot his mouth off about race and such. Four years ago, that sort of thing didn't happen.

Welllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll...

I'd like to point out that the issues Romney chooses here are very specific. He refers to Trump saying things about the "disabled," which Trump didn't do this year, either. Instead, he mimicked the disability of a New York Times reporter who had the gall to point out that Trump was deliberately misrepresenting something he'd reported.

Romney also says "the KKK," which, again, Trump hasn't really said anything about. That was the problem: Trump refused to swear off David Duke (former KKK grand wizard) and white supremacists in an interview and has, at other times, tacitly engaged with white nationalists. By setting the bar at "Trump has to say something approving of the KKK," Romney gets to pretend as though there was no racial undertone to Trump's relentless 2011 insistence that Barack Obama was not born in America. In April 2011, the New Yorker wrote, "What Trump has done (and he is only the latest and loudest and most spectacularly hirsute) is a conscious form of race-baiting, of fear-mongering. And if that makes Donald Trump proud, then what does that say for him?" But, you know. That wasn't about the KKK.

There's also a fairly remarkable interview from 2011 in which Fox News's Bill O'Reilly asks Trump about a number of political topics. At the time, Trump was toying with running for president, eventually deciding against it (thanks, in part, to Obama publicly humiliating him). O'Reilly and Trump talk about all of the things that Romney covered in his tweet (save disabilities).

Why the focus on the birth certificate? Well, Trump says, he figures Obama was may be hiding something. "Maybe it says he is a Muslim," for example.

Earlier in the interview, O'Reilly asked Trump whether there was a "Muslim problem" in the world. Trump notes that he was strongly opposed to the "Ground Zero mosque," a controversy that flared up early in Obama's first term. His answer to O'Reilly's question?

"Absolutely. Absolutely. I don't notice Swedish people knocking down the World Trade Center," he said. As he does, he made sure to praise Muslims, too, but then reversed course. "You have fabulous Muslims. I know many Muslims, and they're fabulous people. They're smart. They're industrious. They're great." But, "unfortunately, at this moment in time, there is a Muslim problem in the world. And, by the way, you know it, and I know it, and some people don't like saying it because they think it's not politically correct."

How does it happen? "I mean, you can say what you want about the Koran. You can say what you want," Trump said, "but there's something there."

He continued in the same vein in further interviews — all in the months before Romney sought his endorsement.

In the interview with O'Reilly, Trump also talked about immigration. His proposal then was to line the border with soldiers who could keep illegal Mexican immigrants out. "They are coming over and they are — they are climbing over a fence, and there's nobody within 10 miles," he said about immigrants. "And they walk — they get a job and they are selling drugs all over the place — they are killing people all over the place. We're not doing anything about it."

To be fair, at the time, he didn't call Mexican immigrants "rapists." That probably would have been too much for Romney.