The Facebook ad purchased by a page called "Angry Buckeyes" in December seemed ordinary at first: It cited a news article that claimed President Donald Trump's tariffs on China could cost Americans.

Facebook has weighed whether to label political ads to indicate that they have not been fact-checked, rather than vetting what candidates say, one of a series of proposals the company has floated to Democratic and Republican operatives as it seeks to head off controversies in 2020 election campaigns.