Donald Trump had a few words for Mitt Romney after the former presidential candidate made the case against the GOP frontrunner this morning. Looking back to when Romney sought his endorsement in 2012, Trump quipped to a crowd in Maine on Thursday: "I could've said, 'Mitt, drop to your knees,' and he would've dropped to his knees."

Trump reminded his supporters that Romney once "begged" him for his support.

Why did Mitt Romney BEG me for my endorsement four years ago? — Donald J. Trump (@realDonaldTrump) March 3, 2016

Romney made an effort on Thursday to unite conservative voters against Trump at his press conference advocating for a contested convention — a strategy that plausibly could lead to Romney securing the nomination.

"If we Republicans choose Donald Trump as our nominee, the prospects for a safe and prosperous future are greatly diminished," Romney said, without endorsing a specific candidate and while urging voters to back whichever candidate had the best shot against Trump in the upcoming contests.

Romney warned that Trump would inevitably fire back with insults, and Trump didn't disappoint.

"[Romney] is a choke artist and I said it very strongly," Trump said. "And then Jeb Bush actually convinced him not to run. Can you imagine? Jeb, Jeb told him. Jeb, he is a good salesman. Jeb is a good salesman. He's a high-energy salesman. But Mitt was afraid of Jeb because he was afraid that Jeb would get the money and Jeb would get whatever. I wasn't afraid. I wasn't afraid of Jeb."

Trump also had a response to Romney's reasoned case against Trump as a businessman, in which Romney called out Trump's failed ventures, from Trump University to Trump Steaks.

"One of the things that Mitt brought up, which is so serious, he said about trade. We have to keep trade, nobody knows more about trade than me. I made so much more money than him," Trump said. "I have a store that's worth more money than him."

"Mitt admitted I'm a much better businessman than him. I am."

Romney, who has one failed attempt at the White House and another failed attempt at the nomination under his belt, was rumored to run for president again but ultimately declined. He has been making his case repeatedly against Trump for weeks, teasing that there might be a "bombshell" in Trump's taxes.

Romney also responded to Trump's claim about begging for his endorsement:

If Trump had said 4 years ago the things he says today about the KKK, Muslims, Mexicans, disabled, I would NOT have accepted his endorsement — Mitt Romney (@MittRomney) March 3, 2016

It's too early to say if Romney's strategy of simply supporting whichever candidate has the best shot against Trump in a given state will work, but it's clear that the lines have been drawn.

And Twitter, of course, had fun with this exchange:

Blow job references, urination jokes, perspiration accusations, spray tan intonations. Your #2016 GOP campaign. — Shane Goldmacher (@ShaneGoldmacher) March 3, 2016

There's so much gay panic in this campaign you'd think George Costanza was running for president. — Nick Confessore (@nickconfessore) March 3, 2016