Former New York City Mayor Rudy Giuliani spent this past weekend calling his 2016 candidate of choice Donald Trump a "genius" for potentially avoiding paying federal income taxes, while adding that voters should prefer him over "a woman." The comments represented the culmination of more than a year of increasingly reactionary rhetoric from a politician who was once widely viewed as a moderate Republican.

Eight years ago, when Giuliani sought the presidency and was an early front-runner, his pro-choice, socially liberal past was seen as a liability. Today, he has become the most aggressive mouthpiece for Trump's world view, doubling down and sometimes extending on the GOP presidential nominee's most controversial assertions.

The question that pundits have been increasingly asking is why? Why would Giuliani risk his brand as "America's Mayor" by aligning himself so unapologetically with the Trump campaign, especially when so many other establishment Republicans have steered clear of it?

The rapid evolution of Giuliani's public persona can actually be traced back to February 2015, months before Trump launched his campaign for the White House. During Black History Month no less, Giuliani generated a firestorm by saying he didn't think President Barack Obama "loves America."

Related: Trump Adviser Giuliani: 'I Wouldn't Participate in Another Debate'

“I know this is a horrible thing to say, but I do not believe that the president loves America,” the former mayor told an audience at a event on behalf of Scott Walker. “He doesn’t love you. And he doesn’t love me. He wasn’t brought up the way you were brought up and I was brought up through love of this country.”

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After Giuliani was intensely criticized for his statement, he established a blueprint that would soon be followed by the Trump campaign: He didn't back down. Giuliani went on to say that the president had been under the influence of Communist ideology since the age of 9. Also, when asked by reporters whether his remarks could been considered racist, Giuliani pointed out that Obama “has a white mother.”

“I didn’t intend to question President Obama’s motives or the content of his heart,” Giuliani later wrote in an op-ed that fell short of an apology. “My intended focus really was the effect his words and his actions have on the morale of the country, and how that effect may damage his performance.”

That March, in the aftermath of protests and riots in Ferguson, Missouri, related to the controversial police shooting death of Michael Brown, an unarmed black teen, Giuliani went where no other major GOP figure was willing to go. He said the shooter, now-retired police officer Darren Wilson, should be "commended" and he used previous actions by embattled comedian Bill Cosby, who is currently being prosecuted for sexual assault, as an example of how Obama should call out his own community.

But few Giuliani watchers could have predicted how active he would be once the 2016 race was in full swing. He has been a ubiquitous presence on behalf of the Trump campaign, which he began publicly supporting in April, often making arguments that even its outspoken standard-bearer wouldn't dare make himself — leading to headlines like Politico's "Is Rudy Giuliani Losing His Mind?"

In addition to enthusiastically standing by Trump's polarizing positions on immigration, such as building a massive border wall and deporting the estimated 11 million undocumented people currently residing in America, Giuliani has:

And then there was his Republican National Convention speech, which has been deemed both fiery and unhinged, depending on your point of view. Framing this current race in apocalyptic terms, a shrieking Giuliani declared, “There’s no next election. This is it! There’s no more time left to revive our great country,” before laying the blame for all the divisions that exist in America, both racial and economic, at the current president's feet.

At the age of 72, with his prospects for national political office likely spent, why would he be spending his days trafficking in conspiracy theories about the Clintons?

Related: Giuliani: Hillary Clinton Was 'Wrong to Attack' Monica Lewinsky in '98

Some have speculated that it may be a settling of old scores. After all, Giuliani was expected to provide fierce competition for Hillary Clinton back in 2000, when she made her first bid for the U.S. Senate in New York, but ironically, health issues forced him to step aside. He was also seen as the likely GOP nominee early in the 2008 presidential race (as Clinton was for the Democrats) until his disappointing campaign came to a screeching halt in the Florida primary.

"He always wanted to battle against her," said Washington Post reporter and MSNBC analyst Robert Costa in August. "He thought New York, national spotlight ... he'd envisioned a race back in '99, he envisioned a race in 2008. It never happened and I think he's been haunted by the lost opportunity."

This has led to speculation that Giuliani may view 2016 as a proxy war, where he can get to participate in the defeat of Clinton is some form. However, that theory would fail to include Giuliani's long personal and financial ties to Trump.

Investigative reporter Wayne Barrett, who has for years made a career out of unearthing the behind-the-scenes machinations of both Giuliani and Trump, portrayed their semi-incestuous political relationship in New York Daily News piece published last month.

Besides the fact that Giuliani now works for a law firm that represents Trump and members of his family, Barrett argues that the two men share similar ideological beliefs and beefs when it comes to minorities, women, as well as questions about their temperament. And he suggests that for both men, this campaign represents a last opportunity to reassert their relevance on a national stage.

" ... [H]e is still treated as a voice of reason, even when he echoes, or inspires, Trump," Barrett wrote. "It is, for both, the last gasp of rapacity, a final dance with grand destiny, propelled by howls of aging ambition."