Sen. Bob Corker. AP Photo/Alex Brandon

Republican Sen. Bob Corker of Tennessee said Friday that his biggest worry is that President Donald Trump is rendering Secretary of State Rex Tillerson ineffective at his job.

Corker, who has been a vocal critic of Trump since announcing in September that he would retire before the 2018 election, told The Washington Post that although he worries about the possibility that Trump will provoke a nuclear war with North Korea and further stoke the conflict with Iran, his biggest worry centers on Trump's relationship with Tillerson.

"You cannot publicly castrate your own secretary of state without giving yourself that binary choice," Corker told The Post.

The choice he was referring to, according to The Post, was deciding between conflict with North Korea or allowing Iran to develop nuclear weapons by pulling out of the Joint Comprehensive Plan of Action, commonly known as the Iran nuclear deal.

Corker sharply criticized Trump earlier this month after Trump tweeted that Tillerson was wasting his time trying to open up diplomatic channels with North Korea, which has grown increasingly provocative in recent months.

"I think Secretary Tillerson, Secretary Mattis and Chief of Staff Kelly are those people that help separate our country from chaos," Corker told reporters at the time when asked about allegations of bad blood between Trump and Tillerson.

Corker added that Tillerson is "in an incredibly frustrating place" where he "ends up not being supported in the way that I hope a secretary of state would be supported."

He doubled down on his support for the secretary of state Friday, saying that while he was concerned about Trump's "very irresponsible" Twitter habits, "it's the first part" — the "castration" of Tillerson — "that I am most exercised about."