In a live-streamed speech, the Vermont senator said that his primary goal is now to "defeat Trump badly."
"The major political task that we face in the next five months is to make certain that Donald Trump is defeated and defeated badly," Sanders told supporters in a live stream video. "And I personally intend to begin my role in that process in a very short period of time."
"Election days come and go but political and social revolutions that attempt to transform our society never end," he said.
"Let me conclude by once again thanking everyone who has helped in this campaign in one way or another," he added. "We have begun the long and arduous process of transforming America, a fight that will continue tomorrow, next week, next year and into the future."