Letterman goes in.

“If we get a president sometime soon who does not have a mental disorder, Twitter will be useful,” Letterman added.

Letterman also said Trump’s feud with civil rights icon Rep. John Lewis (D-Ga.) “broke” his heart.

“He’s ignorant in a way that’s insulting to the office, insulting to America, insulting to human rights, insulting to civil rights, insulting to John Lewis. Trump saying that broke my heart. I thought, ‘You stupid son of a bitch. You ought to have known better than that,’” Letterman said.