The prohibitions include that no person shall knowingly provide "substantial assistance" in the soliciting, making, accepting or receiving of such contributions, donations, expenditures, independent expenditures, and disbursements which are violations of the foregoing prohibitions on foreign nationals.
These prohibitions related to foreign nationals are set out in FEC Reg. 110.20.
I don't know whether the Russian interference in the 2016 elections is being pursued by the Federal Election Commission or by other Federal law enforcement authorities as being a violation of the foregoing prohibitions or whether enforcement of the law is being sought against "foreign nationals" involved in the Russain interference who violated the prohibitions.
In June of 2016 the Campaign Legal Center filed a complaint with the Federal Election Commission that Donald Trump violated the law by sending campaign fundraising emails to foreign nationals — including foreign politicians — in at least Iceland, Scotland, Australia and Britain. See Trump Slapped With FEC Complaint For ‘Illegally’ Soliciting Foreign Money
I don't know whether Trump's asking the Russians to interfere in the election on his behalf (per below video), or other actions and statements by Trump and the Trump campaign, are viewed by the Federal Election Commission or by other Federal law enforcement authorities as "substantial assistance" given by Trump to the Russians in the Russian intererference violating the above prohibitions, or whether enforcement of the law against Trump and the Trump campaign for such "substantial assistance" is being sought.
For earlier discussion, see Smartest colluders.