So it's not a campaign contribution since the insurrectionists weren't a political campaign. If they were involved in supporting a candidate by taking out ads,

So it's not a campaign contribution since the insurrectionists weren't a political campaign. If they were involved in supporting a candidate by taking out ads, there are requirements about declaring the foreign support - but they didn't seem to do that. There is a separate set of laws for conspiracy to commit sedition. If the donor was donating to forment unrest (knowingly) then there are charges that can be pursued, but would likely require extradition.