Asked by CNN's Wolf Blitzer if he would accept a hypothetical offer to be Clinton's running mate, Sanders said he would talk about it with her after the convention.
"Right now, we are focused on the next five weeks of winning the Democratic nomination. If that does not happen, we are going to fight as hard as we can on the floor of the Democratic convention to make sure that we have a progressive platform that the American people will support," Sanders said on "The Situation Room." "Then, after that, certainly Secretary Clinton and I can talk and see where we go from there."
It is impossible for Sanders to win enough pledged delegates in the remaining contests to secure the Democratic nomination, but it remains possible, if unlikely, that Clinton might not win the 2,383 delegates needed for the nomination either, which would set up a potential convention battle in Philadelphia.
"We're going to be in this until the last ballot is cast," Sanders said Friday. Clinton's delegate lead relies in part on the help of more than 500 super delegates -- state party officials and other elected Democrats who can vote for whoever they want -- who support her.
The Clinton campaign and her supporters have struggled to find a successful strategy for pushing Sanders out of the race. Clinton appeared to be gaining momentum after a series of routs in the northeast, including a blowout victory in New York.
But Sanders won an upset victory over her in Indiana last Tuesday.
Most recently, Clinton told CNN's Anderson Cooper
she respects Sanders' decision to finish out the contests.
"I know there are some contests ahead and I respect Sen. Sanders and whatever choices he's making. And I have a lot of empathy about this, Anderson. You know, I ran to the very end in 2008," she said this week.
Asked if he would focus his fire on Donald Trump, with the hopes of helping whoever the Democratic nominee is, Sanders said he would focus on both of them.
"I will continue to run an issue-oriented campaign," Sanders said. "Will I be taking on Donald Trump? Absolutely. Will I be discussing the differences of opinion Secretary Clinton and I have? Yes I will."
Trump tweeted Friday that "Crooked Hillary has ZERO leadership ability. As Bernie Sanders says, she has bad judgement. Constantly playing the women's card - it is sad!"
But Sanders said that was something he never said.
"You read that tweet, that is nothing that I have ever said about Hillary Clinton," he told Blitzer.