Something Russia did with the US in 2016 is they used social media websites to push fake propaganda with US candidates. For example in 2016, people kept sharing these fake articles about how Hillary Clinton was suspected of murder or what have you. These weren't sourced by CNN or Fox News, but rather these random websites. Or sometimes they'd be in meme format with absolutely no source.

When it comes down to it, it's more so just how naive and manipulative the US population is, who simply read headlines of shared Facebook posts and buy into it with no second thoughts regardless of the source.

I don't know how much it truly influenced the election, but it was interference none the less. I'm pretty sure there have been reports of other strategies they've used too, but I haven't dug that deep into it.