Bernie Sanders had one message to his supporters this morning.

“It is absolutely imperative for the future of this country that Donald Trump not be elected president of the United States,” he said on "Good Morning America" today, reinforcing his Tuesday endorsement of Hillary Clinton.

“So, it's about the lesser of two evils?” “GMA” co-anchor George Stephanopoulos asked.

“No, it's not about the lesser of two evils,” Sanders said before listing a number of issues, including minimum wage, college affordability and health care, where he said his formal rival would help working families.



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As for Clinton’s running mate, Sanders said he doubted he would be on her ticket, but that he planned to help her campaign, nonetheless.

“Right now, what my job is to do to make sure that Hillary Clinton is elected president, that we defeat Trump and come up with a set of principles and an agenda that speaks to the needs of working families,” he said.

He added that he was “proud” of the newly finalized platform for the Democratic Party, which was voted on in committee over the weekend. He called it “the most progressive platform in the history of the Democratic Party.”

Sanders did offer some advice for the former secretary of state, who, according to news polls, is neck and neck with Republican presumptive nominee Donald Trump in key battleground states.

“I think what Secretary Clinton is going to have to do is get around the country and contrast her views to Donald Trump's,” Sanders said. “This is not a beauty contest between Trump and Hillary Clinton. This is the fact that the middle class of this country is in trouble. Which candidate has more to say about education, more to say about health care, more to say about climate change … and the more the people hear the contrast between the two, I think Secretary Clinton's support will grow.”

Sanders hesitated to weigh in on the fight between U.S. Supreme Court Justice Ruth Bader Ginsburg and Trump. The justice called Trump a “faker” in an interview published this week.

“I'll let justice Ginsburg answer that herself,” Sanders said when initially asked about it this morning.

“Let me be very clear, I agree with what Justice Ginsburg said. I think that Trump is a total opportunist,” he added. “I do not believe anything that comes out of his mouth, because I think the record is quite clear that he lies just a whole lot of the time.”