No proof, yet. His quick appearance in Ukraine just prior to a major shift in hostilities - involving an operation that required months of planning, involved deep penetration of his enemy's territory, needs to be examined; examined in connection with aggressive statements he has made on the record supporting more aggressive response by Ukr in favor of taking the battle beyond Ukr's borders.
Furthermore, and critically to the point, has he conspired with European groups that have apparently been planning to undermine peace efforts by the present administration.
The Logan Act has raised some questions of Constitutionality; perhaps Graham has just interfered with matters that he should have stayed away from; as a Senator he can judge the validity of foreign policy efforts. To work in shadows to undermine official policy efforts raises many serious questions.

Just swap an image of Bloomy-dwarf for McNoName.
In connection with Lindsey Graham, a phrase like “deep penetration of his enemy’s territory” might be mistaken for a pick-up line.