The former director of the CIA believes Donald Trump could be a threat to national security if he is elected president. Instead, he believes Hillary Clinton is highly qualified to be commander in chief.

Michael Morell, who retired from the CIA in 2013, released an op-ed in The New York Times on Friday citing several reasons he believes a Trump presidency would be detrimental to the safety of the U.S.

In the op-ed, Morell said he spent four years working with Clinton during her run as secretary of state. He hailed her leadership during that time, saying she was "prepared, detail-oriented, thoughtful, inquisitive and willing to change her mind if presented with a compelling argument."

Morell said that in "sharp contrast" to Clinton, Trump's character traits and lack of experience in national security show he's not fit to run a country. He said Trump's call to bar all Muslims from the U.S. would undermine safety, not help it.

Morell specifically finds issue with Trump's views of Vladimir Putin. He wrote Trump has "taken policy positions consistent with Russian, not American, interests," citing Trump's invitation for Russian hackers to find Hillary Clinton's missing emails.

In July, Trump's campaign successfully pushed to keep the Republican party from adding a platform amendment that proposed giving weapons to Ukraine to fight Russian forces in the disputed region of Crimea.

Morell is among several other top government officials to endorse Hillary Clinton, like current U.S. President Barack Obama and Secretary of State John Kerry.

The op-ed serves as his first public endorsement of a presidential nominee.