Five things to know about Trump confidant Tom Barrack
John Kerry: Trump has 'hugely damaged American credibility'
"The president has hugely damaged American credibility on a global basis. He has upset alliances, which are critical to America's long-term security," Kerry told MSNBC.
Kerry said leaders around the world are "worried and wondering what the next shoe to fall may be."
"It is no way to conduct the critical affairs of our nation and I think it puts our interest at risk," he added. "It will cost us both money and, frankly, some of the decisions he's made will cost us lives."
Kerry, the 2004 Democratic presidential nominee, has ramped up his criticism of Trump recently.
He said Sunday that Trump is incapable of governing because he "clearly doesn't understand America."
Kerry also commented last week that the anonymous New York Times op-ed written by a "senior official" in the administration working to thwart Trump's "worst inclinations" means "that we don't really have a president."