Political advertising is flourishing online, but federal guidelines regulating those ads are virtually absent. WSJ's Emily Glazer explains why Facebook, Twitter and Google are making their own rules.

Constitutional experts testified this week on what makes for an impeachable offense, and Democrats and Republicans argued their sides of the case in dueling reports. WSJ's Siobhan Hughes explains.

The world's largest hedge fund, Bridgewater, has placed a massive bet that stock markets will fall by late March 2020. WSJ's Juliet Chung explains its possible motivations.