Robert Gates, the U.S. Secretary of Defense from 2006 to 2011, said Thursday that he would not be comfortable if Donald Trump had control over the launch codes for nuclear weapons.

Gates sounded off on the presumptive Republican presidential candidate during a wide-ranging interview with Yahoo Global News Anchor Katie Couric in New York.

“Would you feel comfortable with his proverbial finger on the nuclear button?” Couric asked.

Gates, who also served as director of the CIA in the early ‘90s, took a deep breath before answering:

“Right now? No. But the question is does he moderate his views on national security issues going forward? Does he begin to have some more informed views about the complexities of some of these issues, some of the challenges that we face? And who does he choose as his advisors? If all of those things turned out in a positive way, then my concerns would be significantly reduced.”

He said the right temperament is perhaps the most important quality for a president. When pressed, he declined to comment on whether Trump or likely Democratic presidential nominee Hillary Clinton would be a better choice based on this criterion.

Former Secretary of Defense Robert Gates discusses Donald Trump’s foreign policy proposals with Katie Couric in New York. (Photo: Yahoo News)

As secretary of defense, Gates served Presidents George W. Bush and Barack Obama, under whom he also worked closely with Clinton when she was secretary of state. He described Clinton as “tough-minded” but said their views started to diverge in spring of 2011, when he opposed and she supported the U.S. intervening in Libya.

“The irony is that the Obama administration made the same mistake in intervening in Libya that the Bush administration made in intervening in Iraq,” he said. “And that was the failure to have a plan for what happens after the intervention, after regime change and to implement that plan.”

He also pointed to Clinton’s email scandal as an example of what he considers her questionable judgment. Clinton exclusively used a private email server for her State Department work. In contrast, Gates said he never used any email for official business when he was director of the CIA or secretary of defense.