The ads, which also appeared on Twitter, show a 30-second video with darkened images of Democratic lawmakers interspersed with bright images of Justice Neil Gorsuch.

Image One Nation, a conservative offshoot of Crossroads GPS, also used Facebook ads to target users in states with hotly contested Senate races.

“Extremists will lie and attack the nominee,” the ad’s narrator says. “But don’t be fooled: President Trump’s list includes the best of the best, and with your help, America will get another star on the Supreme Court.”

Demand Justice, an organization formed this year by veterans of the Hillary Clinton and Barack Obama campaigns, began running Facebook ads on Monday urging voters to “stop Trump’s SCOTUS takeover.” The group, which has said it plans to raise $10 million this year, has also run ads opposing Brett Kavanaugh, Amy Coney Barrett and Amul Thapar, three judges who are reported to be on Mr. Trump’s shortlist for the Supreme Court. The candidate-specific ads began running before Justice Kennedy announced his retirement and were targeted at an audience that included users in California and New York, two Democratic strongholds, but also in Florida, a swing state.

These groups, which are classified as 501(c)(4) advocacy groups, are not required to identify their donors or disclose much of their spending. But new Facebook ad policies are for the first time giving a glimpse of how money from these organizations flows through social media.

In an attempt to avoid a repeat of 2016, when Russian disinformation campaigns successfully exploited flaws in its network, Facebook recently began requiring political advertisers to authenticate themselves as residents of the United States and label every ad with a “paid for by” indication. The company also began archiving all paid political content on Facebook and Instagram, including promoted news, in a searchable public database, along with information about how much was spent on the ads and basic details about how they were targeted.