The Washington Post's Matea Gold and Elizabeth Dwoskin illustrate how Facebook's place in the federal government's Russia probe has shined a light on the secretive nature behind political advertising on the platform.

What's next: "Democratic Sens. Amy Klobuchar (Minn.) and Mark R. Warner (Va.) plan to introduce a bill in the coming weeks that would require sites with more than 1 million users to maintain a public file containing a copy of political ads and information about who they are aimed at."

Why it matters: "The situation has the potential to affect a key profit center for Facebook. The same proprietary technology that has made Facebook the go-to advertising platform for political campaigns also enabled Russian operatives to target U.S. voters with inflammatory ads."

Data point: "By Election Day, Trump's campaign had spent roughly $70 million on Facebook ... nearly all in the last four months of the election."

Be smart:

• You'll see talk online about Facebook "embeds" to the Trump campaign, based on a "60 Minutes" interview with Trump digital director Brad Parscale. The Facebook employees, who had been screened as Republicans, showed up several times a week at Parscale's office in San Antonio.
• "60 Minutes," acting shocked, did a poor job of explaining that these are basically salespeople — provided by the platforms to encourage ad buying.
• The same system was used in the 2012 campaign.