Former Sen. Jeff Flake (R-Ariz.) said in a new interview that he will not vote for President Trump in November, citing concerns going back before the 2016 campaign.

"I just couldn't support [Trump] long before he started to run. The birtherism thing was just too much for me. And then it piled on," Flake, a frequent critic of the president, told The Washington Post.

Flake also said that a second Trump term could turn younger voters away from the Republican Party, pointing to issues including immigration and the environment.

"So for young people who've grown up around minorities or had a different experience than a lot of us in my generation, they don't harbor, I think, some of the prejudices that people in my generation do," Flake said.

He added that a Trump defeat November would be a "long-term" benefit for the Republican Party and "conservatism as well."

"This won't be the first time I've voted for a Democrat - though not for president. Last time I voted for a third-party candidate," he said. "But I will not vote for Donald Trump."

He also predicted that the GOP would change once Trump is out of the Oval Office.

"The pendulum swings when one party takes it too far," he said. "We'll be ourselves again."

Flake, 57, served in the Senate from 2013 to 2019, and was in the House of Representatives for six terms prior to that.

As a senator, he criticized Trump on multiple issues, including the president's negative comments about the late Sen. John McCain (R-Ariz.) in 2015.

Flake was also "shocked" to find out his friend and former House colleague, Mike Pence, was nominated as Trump's running mate in 2016, according to Politico.