as we said, this is a fast-moving story. these developments just happening. it's not the only major development tonight from the whistleblower complaint. a key figure named in it has just resigned. kurt volker is his name. the u.s. special envoy to ukraine. our national security reporter, kiley atwood, joins us now with that. what have you learned about the resignation of this official? >> reporter: well, we should note that kurt volker is probably the key player when it comes to looking at if the state department was helping rudy giuliani a little bit too much with his partisan, politically motivated agenda in terms of encouraging ukraine to investigate joe biden, right. so what we know is that kurt volker had actually met with giuliani. he'd talked with giuliani. he had even, according to the whistleblower complaint, met with zelensky, president zelensky of ukraine, and talked about how to navigate the demands made by president trump over this summer. so clearly kurt volker was in