GOP presidential candidate Donald Trump fired back at long time aide to President George W. Bush, Karl Rove, after Rove appeared on Fox News and wrote an op-ed for The Wall Street Journal titled “Trump and Sanders, the Disrupter Brothers” where Rove bashed Trump’s viability.

Politico reports that Rove appeared on Fox News Wednesday morning and downplayed Trump’s gains in the recent political polls – numbers that put Trump above all other GOP candidates including former Florida Gov. Jeb Bush.

“The fundamentals matter a lot and Mr. Trump’s fundamentals are not good,” Rove said. He added that he thinks Trump will be exposed as not being a serious candidate.

In his op-ed, Rove compared Trump to Missouri Rep. Todd Akin. Akin was bashed for his offensive comments on rape in 2012.

Trump responded to Rove’s comments on Twitter.

Why do people listen to clown @KarlRove on @FoxNews? Spent $430M & lost all races—a Bushy! — Donald J. Trump (@realDonaldTrump) July 15, 2015

.@FoxNews should not put @KarlRove on—he has no credibility, a bush plant who called all races wrong. — Donald J. Trump (@realDonaldTrump) July 15, 2015

Trump has also been critical of Rove in previous years for Rove’s incorrect prediction of the 2012 presidential election results.