On Friday, former presidential candidate Sen. Bernie Sanders (I-Vermont) warned Americans that President Donald Trump may refuse to step down if he loses the November election.

In an interview with Politico, Sanders stressed the possibility of Trump not stepping down. The senator said, “This is not just idle speculation. Trump was saying ‘the only way they can take this election from us is if this is a rigged election.’ Now he is making that statement at a time when virtually every national poll has him behind.”

Sanders then took his message to Twitter in a series of tweets.

Sanders’ concerns stem from a Chris Wallace interview on Fox News Trump participated in back in July. The president said, “I have to see. Look, I have to see.” when asked whether or not he will accept the results. Trump also mentioned delaying the election and how mailed ballots lead to fraud.

Sanders is set to speak about these issues in the coming weeks to help raise awareness about the possibility of Trump refusing to leave the office. He asserted that the priority now is to focus on alerting Americans and then coming up with a plan to tackle the possibility if it were to happen.