Sam Rega/Business Insider
Donald Trump, interviewed by Business Insider in his midtown office.
In the span of 15 minutes, the Republican presidential front-runner referred to Rove as a "total moron" - adding that "you can print that if you want" - and compared him to someone who has worse aim than someone randomly throwing darts.
"A guy like Karl Rove, Karl Rove is Republican establishment. He spent last cycle, $430 million, and lost every single race," Trump said in an interview with Business Insider last week.
"And I saw the commercials and the things that he was making, they're the worst I've ever seen. I thought they were made by the Democrats. So you have morons - but they have morons like Karl Rove. Look at what happened with [Jeb] Bush. Look at what happened."
It was part of a lengthy rant about the so-called GOP establishment in an interview conducted as part of Business Insider's special report on the Trump campaign, "Trump Nation: On the trail with the GOP front-runner."
And on this day, Rove, the former adviser to President George W. Bush, was the poster boy. Trump was raging against an editorial published in The Wall Street Journal last Thursday, which ran alongside an op-ed Rove wrote that criticized the real-estate mogul's debate performance.
"He had, he got zero, no victories, not one. Now, how's that possible?" referring to the 2012 record of the Rove-founded super PAC, American Crossroads. (A Sunlight Foundation study found that just 14% of the money American Crossroads spent went toward supporting winning candidates.)
"It's not even possible. Just throwing darts you do better than that," Trump continued. We have guys like Karl Rove who are really incompetent people. And all you have to do is look at records of people, look at his record. It's a horror-show."
Trump's complicated relationship with the Republican establishment has permeated throughout the 2016 presidential campaign. He frequently rails against party bigwigs in his stump speeches. And for a while, he famously threatened to run as a third-party candidate if the party wasn't "fair" to him - before eventually signing a "pledge" to commit to not running as an independent if he did not capture the GOP nomination.
But Trump also suggested in his interview with Business Insider that if he did, in fact, win the nomination, it would be possible to "make up" with the GOP establishment.
"Maybe. Maybe I will. I can do that too. I can make up with the establishment," Trump said. "Look, the establishment doesn't want me, because I don't need the establishment."
Sam Rega/Business Insider Donald Trump answers a question from Business Insider co-founder, CEO, and editor-in-chief Henry Blodget.
It's another sign that Trump's candidacy, once thought by pundits and party insiders alike to be nothing more than a summer fling, is getting more serious.
Trump was supposed to be a blip on the race. But the "summer of Trump" has lingered well into autumn. And the race has become unsettled enough that a significant bunch of the Republican establishment is beginning to worry about the possibility of Trump or retired neurosurgeon Ben Carson, the two popular "outsider" candidates, earning the nomination.
The success of the pair thus far has flummoxed and flustered fellow GOP rivals, who have openly question how a reality-television star has foiled years, and sometimes decades, of their preparations for the nation's top job.
"On our side, you got the number-two guy - tried to kill somebody at 14," Sen. Lindsey Graham of South Carolina said recently, referring to a story from Carson's memoir, "Gifted Hands," that recounted a youthful violent streak. "And the number-one guy is high energy and crazy as hell. How am I losing to these people?"
And despite the rise of Sen. Marco Rubio (R-Florida), there has been no consensus establishment alternative to come into view. Bush, with his allied super PAC, still has the most resources of anyone in the field - but he has been unable to latch on as a candidate.
For his part, Rove has said in the past that Trump's rise has surprised him. But he questioned whether that surge would last.
Trump, for his part, doesn't think he's going anywhere.
"I'm going to win, I think," he told Business Insider.