Instagram played a much larger role in Russia's efforts to interfere with the 2016 elections than Facebook initially let on. That's one of many striking findings of a bipartisan Senate investigation into Russia's interference in the 2016 election.

The Senate Intelligence Committee released the second volume of its report on Russia's interference in the 2016 U.S. presidential election, and the report makes clear that Instagram played a large role in the Russia-backed Internet Research Agency's "information warfare campaign."

"On the basis of engagement and audience following measures, the Instagram social media platform was the most effective tool used by the IRA to conduct its information operations campaign," the report notes.

This is striking in part because Facebook has long downplayed Instagram's role in Russia's election interference. The company previously told Congress that, according to its estimates, only 20 million people say IRA posts on Instagram (Facebook's general counsel told Congress the IRA reached 126 million on Facebook proper.)

But the Senate report makes clear that the IRA's real influence on Instagram was much higher. The top two most popular IRA Instagram accounts alone generated more than 46 million interactions, according to the report. "In total, over the course of more than two years spent as an instrument for foreign influence operations, 12 of the IRA's Instagram accounts amassed over 100,000 followers, and nearly half of the IRA's 133 Instagram accounts each had more than 10,000 followers," the report says.

In a statement, a Facebook spokesperson acknowledged that its previous assessment of IRA activity on Instagram was "somewhat incomplete," but suggested that some Instagram users who interacted with the accounts in question also interacted with IRA content on Facebook.

"As we said previously, our data regarding the number of Instagram users who were reached by IRA content is somewhat incomplete, but based on the data available, we assess that 20 million unique Americans saw an IRA post on Instagram that didn't see one on Facebook," the spokesperson said.

The Senate report is not the first time questions have been raised about the IRA's use of Instagram. Researcher Jonathan Albright previously found that Instagram was a much bigger source of Russia-backed disinformation than Facebook had previously claimed.

"Facebook’s sibling property has largely been left as an afterthought," Albright wrote in 2017, referring to Instagram. "Instagram is a major distributor and re-distributor of IRA propaganda that’s at the very least on par with Twitter. In my opinion, the platform is far more impactful than Twitter for content-based 'meme' engagement — especially for certain minority segments of the American population." (Facebook subsequently shut off Albright's ability to access data he used in his initial research.)

But the Senate Intelligence Committee's report proves that Albright and others were right to push for more information about the IRA's use of Instagram, which we now know was far more widespread than previously claimed.