>>>We have a treaty with Ukraine, signed by Bill Clinton in 1999, that required mutual cooperation in criminal investigations
What criminal investigation were the Ukranians supposed to cooperate with? Has the DOJ opened an investigation into either Burisma or Crowdstrike?
https://www.politico.com/story/2019/09/25/trump-ukraine-phone-call-transcript-text-pdf-1510770
The President: I would like you to do us a favor though because our country has been through a lot and Ukraine knows a lot about it. I would like you to find out what happened with this whole situation with Ukraine, they say Crowdstrike... I guess you have one of your wealthy people... The server, they say Ukraine has it. There are a lot of things that went on, the whole situation. I think you're surrounding yourself with some of the same people. I would like to have the Attorney General call you or your people and I would like you to get to the bottom of it. As you saw yesterday, that whole nonsense ended with a very poor performance by a man named Robert Mueller, an incompetent performance, but they say a lot of it started with Ukraine. Whatever you can do, it's very important that you do it if that's possible.
Trump is the de facto head of the DOJ. A diplomatic phone call requesting cooperation with the AG is more than sufficient.