He has a thin slice of that. A very thin slice.
His slice is crimes committed by the Trump campaign, in cooperation "with Russia."
Scare quotes, because it is illegal for a campaign to take contributions from any foreign entity. Interestingly, it would be LEGAL for a campaign to buy campaign advertisements from a foreign entity, or even have a foreigner compose a campaign ad, for hire. IOW, they can give money to foreigners, just can't take it.
The broader question of Russians committing crimes is not a question of investigating Trump! That is investigating Russia!
Is it legal to pay a foreigner to create an advertising campaign about the opposition peeing on Russian beds?