WASHINGTON — The Senate Intelligence Committee concluded Thursday that election systems in all 50 states were targeted by Russia in 2016, largely undetected by the states and federal officials at the time, but at the demand of U.S. intelligence agencies, the committee was forced to redact its findings so heavily that key lessons for the 2020 election are blacked out.

The report — the first volume of several to be released from the committee’s investigation into Russia’s 2016 election interference — came just 24 hours after the former special counsel, Robert Mueller, warned that Russia was moving again to interfere “as we sit here.”

It also landed hours after Sen. Mitch McConnell, R-Ky., the majority leader, personally stepped forward to block consideration of a package of election security bills.

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While details of many of the hackings directed by Russian intelligence, particularly in Illinois and Arizona, are well known, the committee’s report describes a Russian intelligence effort more far-reaching than the federal government has previously acknowledged.

It concluded that while there is no evidence that any votes were changed in actual voting machines, “Russian cyberactors were in a position to delete or change voter data” in the Illinois voter database. The committee found no evidence that they did so.

While the report is not directly critical of either U.S. intelligence agencies or the states, it described what amounted to a cascading intelligence failure in which the scope of the Russian effort was underestimated, warnings to the states were too muted, and state officials either underreacted or, in some cases, resisted federal efforts to offer help.