Former Vice President Joe Biden on Thursday gave a sobering takedown of the country's foreign policy under President Donald Trump, saying, "We're walking down a very dark path."

Though hardly mentioning the president by name — referencing him mainly as the president or the administration — Biden tore into the tenets of Trump's "narrow nationalism" during a speech at the Center for Strategic International Studies.

Biden received the Zbigniew Brzezinski Annual Prize — "recognizing and promoting the importance of geostrategic thinking with a transcending moral purpose."

Biden spoke of how the erosion of the middle class over the years spawned a president who represents everything that goes against moral purpose.

"Under these conditions, the appeal to populism and nationalism is a siren song, a way for charlatans to aggrandize their power, raise themselves up, break down those mechanisms that are designed … to limit the abuse of power," Biden said.

"It's not alarmist — we're walking down a very dark path. The isolation of the United States on the world stage endangers, not strengthens, endangers the American people," Biden said.

Biden said the United States' ability to lead in the world has always centered on the "power of our example, not an example of our power."

"For as long as I've been in politics, the United States has earned the respect of the world when we've led with our values," Biden said. "We haven't been perfect … but on balance, the world looked to us, believing that we mean what we say even though we always don't live up to it.

"But today, (there's a) shift to foreign policy that is closed-off and clannish. This administration casts global affairs in a dog-eat-dog competition … a Hobbesian world where for Americans to succeed, others must lose," Biden said.

"Among the many problems plaguing this administration's foreign policy — ideological incoherence, inconsistent and confusing messaging, erratic decision making, unwillingness or inability to solve problems caused by understaffing," Biden said.

Biden asked "when was the last time you could stand in the State Department and yell and hear an echo?"

"You think I'm kidding … it's irresponsible," Biden said. "It's this brand of zero-sum thinking that I find the most disturbing and dangerous.

"The president's vision … is grounded on a disturbing admiration for autocrats and an apparent faith that the world will mistake bluster and bullying for strength. It's built on an erroneous belief that America can go at it alone without our closest friends and allies," Biden said.

"President Trump's 'America First' sloganeering isolates us in a world at a moment, when few if any of today's threats can be met without international effort," Biden said.