Former Vice President Joe Biden on Thursday lamented that the foreign policy approach the Trump administration is taking "endangers" America's interests and America's standing on the world stage.

Biden, giving a Center for Strategic and International Studies lecture in Washington, D.C., said he fears the U.S. is "walking down a very dark path" that "isolates" America from the rest of the international community. Biden said America under President Trump has shifted toward a "theory of foreign policy that is closed-off and clannish," and frames foreign affairs issues as "us and them." Under the Trump administration, Biden said diplomacy is handled with the mindset that, for America to succeed, others must lose.

"This administration casts global affairs in a dog-eat-dog competition," as if it's a competition for who gets to build the latest high-rise structure, Biden said. "It's this brand of zero-sum thinking that I find the most disturbing and dangerous."

Biden also expressed concern that Secretary of State Rex Tillerson's State Department, which has struggled to fill key positions, doesn't have the manpower it needs to perform its functions well. Go to the seventh floor of the State Department, where the highest officials work, and there's an "echo," Biden said.

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"It's irresponsible," the former vice president said.

Biden, who considered running for president in the 2016 election cycle but decided against it after the death of his son, Beau Biden, isn't ruling out a 2020 bid. For now, he leads the Penn Biden Center for Diplomacy and Global Engagement at the University of Pennsylvania. Prior to joining former President Obama's ticket in 2008, Biden served on the powerful Senate foreign relations committee.

Biden said the U.S. cannot go to the United Nations and "wave the flag of narrow nationalism," expressing his displeasure with the U.N. General Assembly gathering last month in which Mr. Trump offered a fiery speech threatening to "totally destroy" North Korea and harshly criticizing Iran.

Biden said the actions the administration is taking are making it more difficult for the U.S. to face current challenges, undermining the country's credibility by planning to back out of the Paris climate deal, questioning the U.S. commitment to NATO and threatening to negate the Iran nuclear deal.

"This administration is calling into question what the word of the United States is actually worth," Biden said.

Biden said China and Russia will rush to fill the vacuum the U.S. leaves on the world stage.