Standing on the debate stage in Detroit last month, Joe Biden surveyed his fellow 2020 Democratic candidates and took the opportunity to aim a barb at President Trump: “This is America, and we are strong and great because of this diversity, Mr. President, not in spite of it."

As the 2020 Democratic front-runner and as vice president to Barack Obama, the first black occupant of the Oval Office, Biden, 76, has consistently championed America's diversity, arguing that its status as a "melting pot" is essential to its strength.

“America’s strength is and has always been rooted in our diversity,” said Biden on Twitter last month. In 2015, Biden opened a White House conference on terrorism by saying, “We are a nation of immigrants, and our strength is that we are a melting pot.”

[Also read: Joe Biden to Trump: 'Divisive' rhetoric is 'causing people to die']

But in 1976, Biden said the opposite and predicted the U.S. might split apart along sectarian lines.

Speaking at an annual Jefferson-Jackson Dinner in Boise in February 1976, Biden said: ”I told you [in a previous speech] about my view that the uniqueness of America didn’t lie in the fact that we’re a great melting pot. We hear that all the time, about it being black and white, rich and poor, Christian and Jew — therefore we’re strong. I told you then, I thought that was a bunch of poppycock.

“The fact we are black and white doesn’t bring us together as a nation. The fact that we’re Christian and Jew doesn’t send us running into one another's embrace to herald our differences. The fact is that people fear differences. The fact that the reason this nation is able to be the most heterogeneous nation in the history of mankind is not because it’s a melting pot. It’s because unlike any other nation in the world, we are uniquely a product of our political institutions.

“If France tomorrow, for example, were to turn in a monarchy, I told you, I did not believe that France would substantively change. Because in France there’s an ethnicity that binds them together, a cultural tie. You don’t have that in America,” he added.

An audiotape of Biden's speech was obtained by the Washington Examiner.

Biden's comments underline his complicated history over race. In 1975, he embraced segregation, saying it was a matter of "black pride." He opposed busing as a means of desegregating schools. In June, he spoke wistfully of his friendship with segregationists in the Senate of the 1970s.

In the Idaho speech, he warned that the country might collapse before the year 2000 if politicians didn’t regain the trust of the American people. It was the year the U.S. celebrated its bicentennial but was still reeling from the Watergate scandal and the resignation of President Richard Nixon in 1974.

"Just look around this country to see how different we are. Unless we get the American people from Delaware to Idaho, Massachusetts to California, believing that the political system can produce results for them, this country is going to spin apart like a gyroscope out of kilter,” said Biden.

“You were saying, ‘No, it can’t happen here, this is America, we’re unique, we are something different.’ Well, the Lord ain’t made a new brand of man in a long time. It can happen here, we can split apart, and we’re moving in the direction of doing just that.

“Without [the public’s] confidence, without their participation in the system, this nation will not see a tricentennial, this nation will not see the year 2000 in a way in which we now think it is composed."

The 1976 speech was not the only time Biden questioned the benefits of diversity. Speaking in New York that same year, Biden claimed diversity “drives us apart” as a society, according to contemporaneous news reports unearthed last month.

“We hear time and again that we are uniquely a melting pot. Because we’re black, white, rich and poor, therefore we’re strong,” said Biden. “The fact that we are black and white, rich and poor drives us apart in America,” he said.