Twitter Inc., the notoriously unfiltered social network that has been called out for doing both too much and not enough to moderate conversations on its service, has entered new territory at a particularly risky time.

After years of staying on the sidelines as U.S. President Donald Trump pushed falsehoods and questionable information on its social media service, Twitter on Tuesday took the unprecedented step of publicly rebutting two of Trump’s tweets. When Trump posted that mail-in ballots would lead to a "rigged election,” Twitter added a link to his posts that brought users to a page disputing the claim.

"Fact checkers say there is no evidence that mail-in ballots are linked to voter fraud,” the company concluded, citing news stories from CNN and the Washington Post, among others.