Social media advocacy isn’t limited to dark money groups, of course. On Monday, the National Republican Senate Committee began running a Facebook ad campaign that consisted of dozens of images of Mr. Trump, along with the label “SCOTUS Action Alert.” The ads, which were seen mostly by older women in Texas, Florida and Ohio, were not posted on the committee’s public Facebook page, but they appeared in Facebook’s ad archive. One Nation, a conservative offshoot of Karl Rove’s Crossroads GPS, also used Facebook ads to target users in states with hotly contested Senate races.
“Our rights hang in the balance,” read one ad, which was targeted to users in Montana, where Senator Jon Tester, a Democrat, is up for re-election. “Tell Jon Tester to help put another great Justice on the Supreme Court!”
The ad was seen fewer than 1,000 times, according to Facebook’s archive.
In addition to building grass-roots support with them, political groups often use social media ads as a kind of instant focus group. In a matter of hours, they can test dozens of variations of ads with small numbers of users, see which one drives the most engagement and use the winning message more widely. In the case of a Supreme Court nominee, social media ads allow advocacy groups to figure out which messages are more effective at energizing their supporters.
But in many cases, there is no indication of who is funding these campaigns.
A Facebook spokeswomen, Elisabeth Diana, said that the company did not require political groups to identify their donors, and that it believed the Federal Election Commission, which monitors political spending, was better positioned to investigate these groups.
“Thanks to the political ad archive, we now know what ads these groups are running, but we still don’t know where the money is coming from,” Mr. Fischer of the Campaign Legal Center said. “That’s a very important consideration. Voters might view these messages differently if they knew who was funding them.”