President Donald Trump responded to Miles Taylor, the former chief of staff to then-Secretary of Homeland Security Kirstjen Nielson, who endorsed presumptive Democratic nominee Joe Biden in a video Monday.

Trump tweeted Tuesday morning that Taylor is a “disgruntled employee” and added that he “never heard of him.”

Taylor criticized Trump in a Republican Voters Against Trump video, describing what he witnessed while working in the Trump administration as “terrifying.”

“You’d go in and try to talk to him about a pressing national security issue. Cyberattack, terrorism threat… He wasn’t interested in those things. To him they weren’t priorities,” Taylor said.

Taylor said Trump cut off aid to California after the Camp Fire in 2018 because “people in the state of California didn’t support him, and politically it wasn’t a base for him.”

“The things he wanted to do, not only were impossible but were in many cases illegal,” Taylor said.

“Even though I’m not a Democrat, even though I disagree on key issues, I’m confident that Joe Biden will protect the country,” he continued.

Taylor’s endorsement was released hours before the Monday kickoff of the Democratic National Convention.

Former First Lady Michelle Obama spoke during the first night of the all-virtual convention, saying that Trump is the “wrong president for our country.”

Trump responded to her speech on Tuesday morning as well, tweeting that he would not have been elected president if not for “the job done by your husband, Barack Obama.”