Former CIA chief John Brennan John Owen BrennanJournalism or partisanship? The media's mistakes of 2016 continue in 2020 Comey on Clinton tweet: 'I regret only being involved in the 2016 election' Ex-CIA Director Brennan questioned for 8 hours in Durham review of Russia probe MORE on Thursday criticized President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE's decision to name White House physician Adm. Ronny Jackson to lead the Department of Veterans Affairs (VA).

In a tweet, Brennan said while he personally knows Jackson and can vouch for his skill as a doctor, he thinks Jackson is unqualified to lead the massive agency, the second biggest in the federal government.

Trump announced his pick of Jackson on Thursday in the same tweet declaring the ouster of VA Secretary David Shulkin David Jonathon ShulkinVA inspector general says former top official steered M contract to friend Schumer demands answers in use of unproven coronavirus drug on veterans Former Trump VA secretary says staffer found plans to replace him in department copier MORE, who had been dogged by accusations of travel abuses.

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I personally know and greatly respect Ronny Jackson....as a terrific doctor and Navy officer. However, he has neither the experience nor the credentials to run the very large and complex VA. This is a terribly misguided nomination that will hurt both a good man and our veterans — John O. Brennan (@JohnBrennan) March 29, 2018

Jackson has served as the presidential physician since 2013, and made headlines in January when he declared Trump had "good genes" after the president's yearly physical.

White House deputy press secretary Lindsay Walters defended Jackson's appointment at a press briefing on Thursday, saying Trump chose him for his long career in medicine.

"As I said earlier, the president has full confidence in Adm. Jackson," Walters told reporters.

"The president did have some early individuals that he was looking at but continuously went back to Dr. Jackson to fulfill this role as VA secretary and ultimately decided that his health care experience, his distinguished career in the medical profession, was something that would be beneficial at the VA," she continued.

Brennan, who served as CIA director during the Obama administration, is a frequent critic of the president who accused Trump of being "unstable" and "unethical" in remarks earlier this month.