Former Secretary of State John Kerry John Forbes KerryThe Memo: Warning signs flash for Trump on debates Divided country, divided church TV ads favored Biden 2-1 in past month MORE said Monday that President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE has massively undercut U.S. credibility worldwide.

"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.

"The President has hugely damaged American credibility on a global basis. He has upset alliances, which are critical to America's long-term security."



– Former Sec. of State @JohnKerry discusses how President Trump has "damaged" global diplomacy with @mitchellreports. pic.twitter.com/zDPyo9ayVT — MSNBC (@MSNBC) September 10, 2018

Kerry said leaders around the world are "worried and wondering what the next shoe to fall may be."

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"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."