Republicans have protested over the past year that election interference is neither unusual nor important. This week’s reports comprehensively put both arguments to rest. Russia waged an unprecedented campaign, targeting Americans across all segments of society, on platforms large and small. The studies do not even cover the entirety of Russia’s online tampering: The hack-and-leak operation that led to the release of Hillary Clinton campaign chairman John Podesta’s private emails, orchestrated by the GRU, Russia’s military intelligence agency, was another crucial salvo in a pro-Trump onslaught.

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Russia’s machinations began more than five years ago. Whether they were decisive in electing Mr. Trump will never definitively be answered. Given the narrow margin of his victory, it is fair to say that any one of several factors ( Ms. Clinton’s campaign missteps, then-FBI Director James B. Comey’s intervention, etc.) was decisive. What can be definitively stated is that all Americans should find this foreign intervention absolutely intolerable.

An essential task now is to prevent its repetition. There is plenty that both Congress and companies can do, starting with modernizing advertising regulations for the digital age. Lawmakers should also create carve-outs to current restrictions on information-sharing that would allow companies to offer data to trusted academics and organizations in a way that preserves user privacy. Platforms should coordinate with one other, as well as with the government, to track manipulation campaigns in real time.

The Senate Intelligence Committee has said it does not necessarily endorse the findings of this week’s reports, but its bipartisan decision to commission the reports is encouraging. The question now is whether committee members will be willing to hold Russia accountable in their own forthcoming review. Candidate Donald Trump once invited Russia to find Ms. Clinton’s emails, sending the message that it could meddle with impunity. Though sanctions have been imposed since the election, evidently Russia has not been deterred. Until that changes, no reform will be sufficient.