'Too Late to Protect 2018 Elections,' says Alex Stamos, former Facebook CSO

I’ve been following the Concord Management trial (one of the indicted “Russian entities”). It seems that there is no specific US law against a foreign company (whether Russian, Saudi or Israeli) doing this sort of thing, as long as they are not explicitly promoting a candidate. The charge is an elaborate theory based on conspiracy law which I could not explain in 100 words.
If the US wants this to be illegal, why don’t they pass a specific law?