Columnist and Fox News contributor George Will is no fan of Donald Trump. In December, he made his feelings crystal clear in a Washington Post column in which he summed up all of the GOP front-runner’s disagreeable human traits:

If you look beyond Donald Trump’s comprehensive unpleasantness — is there a disagreeable human trait he does not have? — you might see this: He is a fundamentally sad figure. His compulsive boasting is evidence of insecurity. His unassuageable neediness suggests an aching hunger for others’ approval to ratify his self-admiration. His incessant announcements of his self-esteem indicate that he is not self-persuaded. Now, panting with a puppy’s insatiable eagerness to be petted, Trump has reveled in the approval of Vladimir Putin, murderer and war criminal.

There was no chance that Trump wouldn’t respond to that sort of criticism, but rather than break out the thesaurus, Trump has been taking shots at Will’s eyewear, which he did again today at his rally in Ottumwa, Iowa.

The bespectacled Will has warned that conservatives’ “highest priority now must be to prevent Trump from winning the Republican nomination” in order to avoid guaranteeing another Democratic president and the end of the conservative party. Trump, in turn, has warned his supporters not to listen to Will.