MUNICH — Speaking on German soil 75 years after the U.S. and its allies prepared for D-Day, Joe Biden described America as "an embarrassment" and its trade policies "self-defeating."

"The America I see values basic human decency, not snatching children from their parents or turning our back on refugees at our border. Americans know that’s not right,” the former vice president and potential 2020 Democratic presidential candidate told the Munich Security Conference. "The American people understand plainly that this makes us an embarrassment. The American people know, overwhelmingly, that it is not right. That it is not who we are."

Biden, 76, speaking at the annual gathering of foreign policy leaders, didn't mention Trump by name. But, despite a longstanding tradition of politics "stopping at the water's edge" and refraining from criticizing a commander-in-chief while on foreign soil, Biden took the opportunity to blast him, even veering into criticism of domestic policy as he launched into what sounded like a stump speech.

The former vice president was speaking exactly three-quarters of a century after American troops were fighting against Germans at the Battle of Anzio and Allied military staffs were deep into planning for the D-Day invasion of Normandy less than 4 months later.

Biden said: "While I cannot speak today as an elected government official who is able to set policy, I can speak as a citizen. I can offer insight into my country. I know we’ve heard a lot today about leadership, but in my experience, leadership only exists if somebody — and others — are with you. Leadership in the absence of people who are with you is not leadership.”

That concept of American politics ending at "the water's edge" was formulated in 1947 by Sen. Arthur Vandenberg, a Republican from Michigan who was then the Senate Foreign Relations Committee chairman. He was urging President Harry Truman to take a bipartisan approach to foreign policy.

[Related — Dueling vice presidents: Pence and Biden joust in Munich over foreign policy]

Biden’s jabs drew applause from European critics of Trump hours after Vice President Mike Pence had spoken at the conference lauding the president's efforts to press NATO allies to increase defense spending in the face of Russian aggression.

Ironically, Biden lambasted Trump at the high-profile conference for making his grievances with allies public. “You’re never allowed to disagree with your brothers and sisters in public,” he said. “Today, because of, I think, a lack of leadership coming from the other side of the Atlantic, we find ourselves in a different place,and it’s uncomfortable.”

Biden alluded to limbering up for a bid for the 2020 Democratic nomination, which would be his third tilt at White House, after sputtering attempts in 1988 and 2008. “I have spent the better part of the last two years traveling throughout the United States of America, from Minnesota to Texas; from Boston to Birmingham,” he said. “I can assure you, that the American people, the ultimate wellspring of power in the United States of America, remain committed to engaging the world with decency and respect.”

He added, “Those same people who I met all across the United States, who may feel disconnected, discounted, ignored, or left behind ... They still believe, as I do, that the core values enshrined in our alliances are worth defending.”

[Read more: Trump is heir to John McCain, Mike Pence tells Europe]