Facebook chief executive Mark Zuckerberg has promised to make political advertising more transparent. (Steven Senne/Associated Press)

EARLY THIS month, Facebook announced the first hard evidence of Russian efforts to spread disinformation over social media during the election: 470 fake accounts and pages, which paid $100,000 to run thousands of advertisements apparently designed to heighten political tensions. Now, after weeks of uncertainty, the company has made the correct decision to share the ads with congressional investigators probing election interference. Next it should do the same for the public.

The company first argued that federal privacy law prevented it from sharing the ads and fake accounts. While it handed over the material to special counsel Robert S. Mueller III, likely after he acquired a warrant, it balked at providing copies to the House and Senate intelligence committees. Now, Facebook says its legal obligations don’t prohibit disclosure after all. It’s giving Congress not only the advertisements, but also user information belonging to the fake accounts, along with the terms the advertisers used to target particular Facebook users. The latter may be particularly important as investigators examine whether the ads aimed to influence particular groups of voters by location, demographic and interest in certain topics. For example, did the Kremlin seek to push voters in certain areas of the country to support President Trump by showing them anti-refugee propaganda?

Facebook’s decision to provide Congress with ad information is an important step. But while reporting has revealed some samples of the fake accounts, Facebook has declined to make public any information about what the advertisements looked like or what messages they distributed.

Facebook argues that handing the advertising information to Congress is the best way to provide a public accounting of Russian election interference, reasoning that congressional investigators are best positioned to interpret Facebook’s data in the context of sensitive intelligence. It’s true that members of the public don’t have the same insight into election interference as the intelligence committees do. But it will take time for the committees to complete the thorough investigation that is needed and to release their findings. While the investigators work, the public should be able to begin an informed discussion about how a hostile foreign power sought to undermine American democracy by warping its citizens’ behavior.

Though Facebook is right to be careful about distributing material that might raise privacy concerns, an advertisement is public by nature. Facebook might choose not to make public potentially sensitive account information or targeting data, but it’s hard to see what’s keeping it from releasing ads that have already been displayed to thousands — if not millions — of users.

Alongside its announcement about sharing information with Congress, Facebook released a promise to continue its internal investigation into misuse of its platform and a commitment to greater transparency in the ads it runs. This is an encouraging sign of its willingness to think of itself as a partial custodian of democratic debate, as more and more Americans receive their news from social media. That willingness also requires swifter accountability to the public.