Despite Trump's impeachment, Giuliani doubles down on controversial Ukraine push The president's personal lawyer has continued to pursue controversial theories.

Rudy Giuliani, President Donald Trump's personal lawyer and confidant, is doubling down on the tactics and arguments that ultimately contributed to the impeachment of his most prominent client.

Even while facing legal scrutiny from federal prosecutors in New York, according to sources -- and with the president headed for trial in the Senate -- Giuliani has only raised his profile.

First, in the middle of impeachment proceedings, Giuliani returned to Ukraine -- and resumed investigating Democrats and the son of former Vice President Joe Biden, who is vying to run against Trump in the 2020 election.

The former New York City mayor has been at the center of the impeachment firestorm that erupted after a whistleblower complained about a Trump phone call with newly elected Ukraine President Volodymyr Zelenskiy in July. Witnesses who testified before Congress contended that they were directed to work with Giuliani at the president's behest to get the government to announce investigations into the Bidens.

And then this week, Giuliani revived the conversation about unproven allegations of political corruption in Ukraine involving Biden’s younger son, Hunter. Giuliani's personal Twitter feed revved back up, promoting a film he made with a conservative news outlet that accompanied him on his journey.

Giuliani triumphantly announced this week -- the same week that his client was impeached -- that his investigation in Ukraine uncovered fresh evidence to support his theory. And although he has yet to publicly provide any details about this alleged evidence, Giuliani declared that he intends to submit his findings in a "report" to the Justice Department.

At this point, Giuliani has emerged as one of the most durable allies of Trump’s presidency. The former mob-busting federal prosecutor became a close adviser to Trump during his campaign, and was briefly rumored for a prominent cabinet post before he agreed to serve as one of the president’s small clutch of private attorneys.

Giuliani first surfaced publicly as a principal character in the Ukraine scandal back in March, when he announced he had scheduled, and then abruptly canceled, a trip to Kyiv.

He said he wanted to urge Zelenskiy , the new Ukraine president, to open investigations into two matters that Giuliani said he was extremely concerned about -- the origin of the special counsel's investigation into Russia’s meddling in the 2016 election, and Hunter Biden’s involvement in a gas company called Burisma. Both involved theories that have not been proven.

His insistence came despite the intelligence community's clear assessment that Russia was responsible for the election meddling.

At the Kremlin's direction, Russian intelligence services waged a pro-Trump disinformation campaign on social media and secretly stole tens of thousands of private emails from the Democratic National Committee, the U.S. intelligence community concluded.

Giuliani's contacts with Ukrainian officials became a centerpiece of the impeachment hearings, with witnesses describing his efforts as a shadow diplomacy campaign meant purely for the president's political gain. Career diplomats testified that those efforts, which involved withholding security aid from Ukraine, ran counter to U.S. policy.

Giuliani's actions figure prominently in the House Intelligence Committee's report on impeachment -- which describes how he publicly implored Ukraine for months to initiate the investigations, waging a smear campaign against the former Ukraine Ambassador Marie Yovanovitch, who he believed stood in the way of the investigations, and traveling to Ukraine to urge officials there to cooperate.

He appears to be resorting to the same tactics once again, and some who know his work have begun debating what exactly is fueling Giuliani’s latest resurgence.

“There is a possibility that there is a method to the madness,” an attorney who used to work with Giuliani, who did not want to be named, told ABC News. Although Giuliani’s recent behavior may seem unorthodox, the source said that these tactics would not be an “unprecedented strategy” for an attorney to take defending a client.

“Rudy is blurring the line between diplomacy and a non-government official,” Giuliani’s former associate continues. “He is doing everything in his power to defend his client and establish his innocence.”

However, some senior White House officials told ABC News they have “great frustration” with Giuliani’s public commentary and that they wish he would “just go away and never be seen in public relating to any of this again.”

When asked by Fox News to respond to the ABC News report, Giuliani said his critics in the White House are just “buying into the Democratic spin.”

“The fact is, there’s no doubt there are some differences in opinion inside the White House about Rudy Giuliani’s usefulness in all of this,” former New Jersey Gov. Chris Christie, an ABC News contributor, said. “One person who doesn’t have any doubt about it at the moment is the president of the United States. I can tell you he supports Rudy Giuliani wholeheartedly and what he’s doing.”

Indeed, the president continued to praise Giuliani’s work this week.

“He’s a great person who loves this country, and he does this out of love, believe me,” President Trump said of Giuliani on Monday.

Despite not being a member of Trump’s administration, Giuliani is quick to tout his influence on the president. In recent days, Giuliani has publicly boasted that he was a key player in ousting Yovanovitch, who Giuliani claims blocked investigations into the Bidens and Democrats.

“I forced her out because she was corrupt,” Giuliani said of Yovanovitch on Fox News Monday. In fact, there was no evidence Yovanovitch was recalled for this reason, and multiple colleagues from the state department attested to her reputation as having worked to stamp out corruption. When asked why he served as point man on terminating Yovanovitch instead of Secretary of State Mike Pompeo, Giuliani avoided the question, diverting the conversation back to his allegations of corruption by the Bidens and Democrats in Ukraine.

Even after the impeachment hearings, Giuliani has continued to push the false narrative that Yovanovitch had done wrong, alleging again without evidence that she perjured herself during that October testimony.

Meanwhile, Trump has continued to encourage his lawyer to dig deeper into Ukraine, according to Christie, who remains close to Trump. Christie said the president enjoys seeing Giuliani’s “aggressive posture.”

“I don’t believe that Rudy Giuliani would be doing much of what he’s doing [unless] … the general approach is one that I have to believe is approved by the president," Christie said. "They are very close.”

Shanlon Wu, a former federal prosecutor turned white-collar criminal defense attorney, agrees with Christie.

“Giuliani is making it obvious that he’s involved in foreign policy, which he could not do without President Trump’s permission,” Wu says. “It might not be illegal, but it is certainly improper."