Rudy GiulianiRudy GiulianiTrump attacks on Vindman trigger backlash AP: Saudi tycoon donated to Obama inauguration through a middleman House committees ask key Mulvaney aide for testimony in impeachment inquiry MORE on Wednesday swiped at President TrumpDonald John TrumpNumber of uninsured children rises for second year, tops 4 million Trump moment from White House Halloween trick-or-treat event goes viral White House official says transcript of Ukraine call omitted key phrases: report MORE's nominee to serve as ambassador to Russia after he said in a confirmation hearing that Giuliani was involved in a "campaign" opposing the administration's former ambassador to Ukraine.

Giuliani hit back at Deputy Secretary of State John Sullivan in a pair of tweets, claiming Sullivan "doesn't know what he's talking about and shouldn't be incorrectly speculating."

"This is an orchestrated attempt to harass and hinder me in my role as @realdonaldtrump's attorney," Giuliani tweeted. "All of the information I obtained came from interviews conducted as private defense counsel to POTUS, to defend him against false allegations."

Giuliani claimed he began obtaining that information as early as fall 2018.

...private defense counsel to POTUS, to defend him against false allegations. I began obtaining this information while Mueller was still investigating his witch hunt and a full 5 months before Biden even announced his run for Pres.

It won’t work!

— Rudy Giuliani (@RudyGiuliani) October 30, 2019

Giuliani's activities are at the heart of House Democrats' impeachment inquiry into whether Trump abused his office by pressuring foreign governments to investigate a domestic political rival.

Asked about the administration's dealings with Ukraine during Wednesday's confirmation hearing, Sullivan told lawmakers Wednesday that he was aware of a “campaign” against former Ambassador Marie Yovanovitch by Giuliani.

"I was aware that Mr. Giuliani was involved in Ukraine issues," Sullivan said. "My knowledge, particularly in April, May, June timeframe even into July was focused on his campaign basically against our ambassador to Ukraine."

Sullivan also told lawmakers that he became aware of a packet of information about Yovanovitch that was supplied to the State Department counsel. He said it was told he came from “someone at the White House” but that he didn’t know who was responsible for producing the packet.

Democrats who reviewed the documents described them as “propaganda” and “disinformation.” Giuliani told NBC News earlier this month that he gave the information to Secretary of State Mike PompeoMichael (Mike) Richard PompeoOvernight Defense: House approves Turkey sanctions in rebuke of Trump | Trump attacks on Army officer testifying spark backlash | Dems want answers from Esper over Ukraine aid Menendez seeks probe into if Pompeo violated Hatch Act House approves Turkey sanctions in rare bipartisan rebuke of Trump MORE and that he was told State would look into them.

Sullivan's testimony corroborated some of what Yovanovitch told House lawmakers in a closed-door hearing earlier this month.

Yovanovitch said in her opening statement that she was informed that there had been a "concerted campaign" against her since Summer 2018 but that she had done nothing wrong.