First of all, no he isn’t. In fact, it’s illegal for the US government to supply arms that might be used in the commission of war crimes. In this case there’s not even any doubt.
As for the GOP, they’ve already demonstrated that whether or not they try to impeach has nothing to do with reality. Even if they DID somehow manage to make impeachment stick by a one-vote majority, there’s literally no risk that 2/3 of the senate will vote to convict, so that’s not anything remotely resembling a valid excuse to keep contributing to a genocide either.