California Republican Devin Nunes is at the center of a frenzied uproar in Washington with Friday's release of a secret memo on FBI surveillance.

The controversy comes with the 44-year-old chairman of the House intelligence committee on a rocky, rapid rise to power in President Trump's Republican Party — an ascent that required something of an about-face. Once an aggressive critic of the GOP's populist right flank, Nunes has become a key Trump defender and champion of the party's most conservative wing.

Nunes began his congressional career at age 29, under the wing of former Rep. Bill Thomas, R-Calif., the powerful and respected chairman of the tax-writing House Ways and Means Committee. Nunes befriended Thomas, and his staffer Kevin McCarthy, years earlier when Nunes served on the board of a local college.

Thomas nurtured Nunes' career, helping him earn a seat on the Ways and Means Committee. Five years later, McCarthy was elected to fill Thomas' House seat and immediately became part of a powerful political alliance with Reps. Eric Cantor, R-Va., and Paul Ryan, R-Wis., known as the Young Guns. That trio was the face of a new generation of political conservatives and by 2009 all three were in House leadership. Nunes was one of their closest allies.

In the years since, McCarthy was elected House majority leader, Ryan became speaker, and Nunes was selected to lead the House intelligence committee. He also remains a prominent member of Ways and Means, where he helped craft last year's sweeping tax code overhaul.

His power and style evolved as he rose to prominence within the House GOP. In 2013, he famously criticized members of the Tea Party for forcing a government shutdown over what he called an unreasonable demand to repeal the Affordable Care Act. Nunes was quoted in a Washington Post article at the time calling those far-right members "lemmings with suicide vests."

But all that changed in the era of Trump.

Nunes served on Trump's transition team and has been one of the president's most ardent defenders.

Here are the five key factors you need to know to understand Devin Nunes' role in the Russia probe and the secret memo released Friday.

1. Nunes rose to prominence during House investigation into Hillary Clinton's emails.

The House Intelligence Committee was involved in the probe into Hillary Clinton's use of a private email server while she was serving as secretary of state under President Barack Obama. Nunes pressed for detailed information on Clinton's handling of classified information throughout the investigation, ultimately floating the idea that Clinton and her presidential campaign could be denied classified briefings.

"Should Hillary Clinton's staff be given classified briefings at this point? I think it is a question that needs to be answered," Nunes said in an interview on Fox News.

That interview came nine days before the election and amid the firestorm over the decision by former FBI Director James Comey to announce that he was reopening an investigation into Clinton's emails.

2. Nunes got close to Trump during the election and as a member of the Trump transition team.

Many political analysts point to the 2016 presidential campaign as the moment when Nunes began to shift from a GOP traditionalist to a loyal ally of Trump's populist movement. Nunes offered intelligence briefings to all of the Republican candidates in 2016, and Trump took him up on that. The two forged a bond as they traveled around California in Trump's campaign plane.

Nunes and Trump attended fundraisers and rallies across the state, working closely on an unlikely bid to rally the intensely Democratic state behind Trump's campaign. Within days of the election, Trump named Nunes as a member of the executive committee that would run his transition.

3. Nunes and his Democratic counterpart on House intel were once close, but now Democrats want him removed.

The Russia investigation on the House intelligence committee started as a bipartisan affair. Chairman Nunes and ranking Democrat Adam Schiff, a fellow Californian, were once said to have a "bromance" by the San Jose Mercury News. They bonded over their shared love of the Oakland Raiders NFL team and set out to make their probe into the 2016 election a friendly affair.

Things were going well in early 2017 when the two appeared at one of their first joint news conferences on their investigation. Schiff and Nunes stood side by side on March 15 as Schiff told reporters that they were working together.

"The chairman and I are doing everything we can to keep this investigation bipartisan or nonpartisan, to make sure we follow the evidence wherever it leads," Schiff said. "That is certainly our hope and will continue to be our effort to do so."

That all ended as the probe devolved into an all-out partisan brawl, involving ties between Nunes and the White House. The two sides are at war over the release of the memo, and House Minority Leader Nancy Pelosi and Senate Minority Leader Chuck Schumer have both called on Ryan to remove Nunes as chairman of the intelligence committee.

4. Nunes is no longer in charge of the Russia investigation because of his close ties to the White House.

Nunes was forced to recuse himself from the inquiry, while remaining House intelligence chairman, amid controversy over a meeting he had at the White House about a secret source who purported to have evidence that the Obama administration illegally tapped the phones at Trump Tower. No evidence of that has emerged. Nunes said he has learned of "dozens" of classified reports that detailed the surveillance of Trump transition officials, which is the crux of the controversial memo release.

Democrats and even some Republicans criticized Nunes over concerns that he was coordinating with the White House rather than conducting an independent investigation. The news led Schiff to break off the nonpartisan approach and ask for Nunes to step aside.

"This is not a recommendation I make lightly, as the Chairman and I have worked together well for several years; and I take this step with the knowledge of the solemn responsibility we have on the Intelligence Committee to provide oversight on all intelligence matters, not just to conduct the investigation," Schiff said in a statement.

Criticism of Nunes poured in, including from GOP senators like John McCain and Lindsey Graham, who worried the entire House investigation had been compromised.

Graham told NBC's Today that Nunes' behavior was "bizarre."