Sen. Bernie Sanders, I-Vt., provided the Democratic Party with an "autopsy" Monday night, explaining what progressives must do to succeed in future elections.

"What it would say, is the Democrats, the Democratic Party, cannot continue to be run by what I call the liberal elite," Sanders said said to the Late Show's Stephen Colbert, repeating messages sent out on his Twitter account around the time the interview was taped in New York.

Colbert asked if the unsuccessful 2016 Democratic primary presidential candidate, in town to do PR for his new book, views himself as one of those elites. Sanders said he does not and continued with his prognosis of the party before coming back to pitch his new book.

"Good-meaning people, they're not my enemy, they're partners of ours. But the party has got to transform itself to be a party, which first of all, opens the door, that is a party that feels the pain of the working class, of the middle class, of low-income people, of young people - brings people into the party on every - virtually every issue that I talk about in that book," said Sanders.

The unsuccessful presidential candidate had endorsed Hillary Clinton as the nominee despite leaked emails in July that indicated Democratic National Committee Chair Debbie Wasserman Schultz and CNN contributor Donna Brazile had colluded with Clinton's team to boost Clinton for the nomination. Prior to the convention, Sanders had campaigned against the wealthiest of Americans, even attacking Clinton for protecting Wall Street and giving private speeches to large corporations and banks.

The senator's about-face in July came at the same time he told Colbert he decided to write a book about his experiences, which includes ideas on how to unite the frustrated party.

Although the 464-page "Our Revolution" was sent to the publisher well before last week's historic election, Sanders focused much of the book on why he is hopeful the party will unite, just like Republicans did in 2012 when a second loss to President Obama caused conservatives to undertake their own official autopsy.

Sanders spent two-thirds of the book speaking optimistically about the future, giving some indication he is not ruling out running for president again in 2020.

"The vast majority of the American people are on our side. Trump's views are a minority," Sanders told Colbert, giving himself more support for a future run. He claimed raising the minimum wage, ensuring pay equity for women and men, and giving free tuition to public colleges are areas the public would overwhelmingly support.

Despite Sanders' statement that most Americans are on Democrats' side, last week's presidential election results tell a different story. While 61 million voted for Clinton, 60 million backed Trump. In addition, Republicans were supported in the majority of House and Senate races, allowing them to maintain their majorities in Congress.

Sanders' book will be released Tuesday.