Doesn't it seem even a bit unusual for a Ukrainian arms dealer to be hosting a fundraiser for someone like Rep. Schiff? Isn't that the kind of interaction that might lead to questions about security clearances?
Take a look at the background of Pasternak, Alexandra Chalupa, and Melanne Verveer.
You can start here or here, or here, or with Ms. Verveer's wikipedia article here
Along the way it is worth learning more about Ivanna Voronovych.