On Monday night, retired Lt. Col. Alexander Vindman told NBC Nightly News host Lester Holt that he now is now absolutely a “Never Trumper,” after the president’s relentless attacked on him for months.

Vindman, a former National Security Aide who had been the Democratic’s key impeachment witness, has been bullied by President Donald Trump online for months. In July, Vindman retired from the Army, releasing a scathing statement that accused the president of running a “campaign of bullying, intimidation and retaliation,” after Trump had launched a “vindictive” campaign to block his promotion to full colonel.

Immediately after Vindman appeared before the Democratic-controlled House to publicly testify against Trump in the impeachment hearing, the president called him a “Never Trumper” on Twitter.

During the interview Monday night, Vindman accused Trump of threatening national security interests and claimed that he is speaking out publicly to encourage Americans to “choose an alternative” to Trump.

Holt had also pressed Vindman, “The president suggested you are a Never Trumper. Are you a Never Trumper?”

Vindman replied, “I joined this administration, the president’s team, well into the administration with the hopes of being able to do my job, with the hopes of being able to advance U.S. national security interests. I can say now that I am a Never Trumper. I was not a Never Trumper before.”

He continued, “I was nonpartisan. Regardless of what administration, I would just try to do the best I could to advance national security interests, but I think as the president’s attacked and politicized me directly, and in taking a very sober view of where the president has taken this country—the divisions, catering to our adversaries, the undermining of our national security interests, that I am absolutely a Never Trumper.”

Vindman, an Iraq War veteran, said that he is speaking out with “a significant amount of personal risk.

The former lieutenant colonel hopes to “inform an electorate going into the most important election of our lifetime, and maybe persuade them to choose an alternative to what we have.”

“We cannot have four more years of this president and the kind of damage that he’s done to American institutions. We have other choices,” Vindman said. “And frankly, it’s a binary choice. It’s one or the other. We can’t sit out on the fence.”

Nonetheless, Vindman refused to comment on his voter registration status as either a Democrat or Republican this year, keeping the information condifential.

“I can tell you this: that the choice for me is clear…. I’m going to be voting for the other guy.”