WASHINGTON » In a cozy corner of loftlike offices near Union Station, 16 young researchers sit almost shoulder to shoulder, monitoring rows of computer screens.

Their mission: Track attacks on Hillary Rodham Clinton, defend her record and dig up any potentially damaging information on her would-be 2016 rivals. Their leader: the one-time Clinton antagonist David Brock.

While Clinton says it is far too early for her to consider a run for the presidency, a sprawling and well-funded operation built by Brock has already established a rapid-response nerve center for her.

Brock is determined to defend and define Clinton’s image during her candidacy-in-waiting the kind of task her aides have struggled with since her earliest days in Washington.

Back then, Brock was a self-described conservative hit man intent on taking down the Clintons. He famously went to Arkansas in 1993 and wrote an article for a conservative magazine asserting that state troopers had facilitated sexual liaisons for Bill Clinton, then the governor, which led to Paula Jones’ 1994 sexual harassment lawsuit against Clinton and Brock’s elevation in Republican power circles.

On Tuesday, Brock returned to Arkansas for the first time since that article, this time in the warm embrace of Clinton world: He delivered an address, titled "Countering the Culture of Clinton Hating" to a packed audience at the Clinton School of Public Service in Little Rock.

Part confession, part cautionary tale, Brock took the stage of the converted railway station adjacent to the William J. Clinton Presidential Center to talk about his involvement in "The Arkansas Project" in the 1990s, or what he called a conservative-funded "dirt digging operation into the Clintons’ past."

He warned of a similar type of animus toward Hillary Clinton as she contemplates another run for the presidency. On one hand, he said, there will be "a voracious news media hunting for any Clinton crumb, and on the other, well-funded anti-Clinton mudslinging operations that feed the beast."

Brock singled out Sen. Rand Paul, R-Ky., as the "poster boy for this retro strategy" because of his recent criticism of Bill Clinton’s involvement with Monica Lewinsky. A spokesman for Paul declined to comment.

The Clintons have no official role in Brock’s empire, but, along the way, as he has abandoned his right-wing roots and sought to expose what he views as the conservative machinery he was once a part of, they have encouraged his efforts.

On Monday night before his speech, Brock was back at the Capital Hotel on West Markham Street. The last time he was at the wood-paneled bar, Brock, 51, said he was "still in my 20s, drinking" and "plotting a campaign of dirty tricks" to stop the Clintons. This time, he socialized with Skip Rutherford and Bruce Lindsey, two of Bill Clinton’s oldest friends and aides.

"In the 1990s, this guy was as rough and tumble as they get," Rutherford said in an interview. "I don’t know if this is a walk through nostalgia or waking up from a bad dream, but today David Brock reintroduces himself to Arkansas."

In 1996, Brock wrote a flattering biography of the first lady and, later, publicly changed his political affiliation. His 2002 book, "Blinded by the Right: The Conscious of an Ex-Conservative," provided a firsthand account of his evolution and resonated with the former president. Bill Clinton was known to hand out copies of Brock’s book as proof that the "vast right-wing conspiracy" (a term Hillary Clinton used in a 1998 television interview) existed.

The "super PAC" Brock founded, American Bridge, has tapped into the rich network of Clinton supporters. Among them, according to federal disclosures, are George Soros; Steve Bing; Stephen M. Silberstein, a Bay Area entrepreneur; and Susie Tompkins Buell, a friend of Hillary Clinton’s based in San Francisco.

Last year, Bill Clinton delivered the keynote address at a fundraiser in New York for Brock’s biggest donors. Brock thanked the former president and Hillary Clinton for "giving me the gift of forgiveness," said one person who attended the fundraiser, which was closed to the news media, but could not discuss the event for attribution.

These days, Brock has a gray pompadour, and often dresses entirely in black, making him a conspicuous presence in the Brooks Brothers world of political operatives here. He splits his time between Washington and the West Village in Manhattan, and he works in an open office with Toby, his schnoodle (a poodle-schnauzer mix), at his side.

He now has about 165 employees working for American Bridge and the separate nonprofit organization he founded, Media Matters, which monitors conservative bias in news reports and often takes aim at Fox News. And while American Bridge provides rapid response and tracking to help get Democrats elected, Brock has started a new initiative within it, called Correct the Record, to focus exclusively on 2016 and defending Hillary Clinton.

Combined, Brock’s organizations brought in $25 million in donations last year, he said.

The speech on Tuesday, in which he apologized for his early attacks on the Clintons, marked a full-circle evolution for the man whose answering machine during the mid-1990s said, "I’m out trying to bring down the president."

But people close to Brock have said his ultimate mea culpa would be to help get Hillary Clinton elected president. He serves as an adviser to Ready for Hillary, a political action committee focused on grass-roots outreach, and is on the board of Priorities USA, the big-money fundraising vehicle devoted to a Clinton candidacy.

Not everyone, of course, views Brock as trustworthy, and some conservatives called him a "switch-hitter" who employs the same tactics he once used against the Clintons against their enemies.

"I was astonished he’d go over to the other side and make a handsome profit on kissing and telling," said R. Emmett Tyrrell Jr., editor in chief of The American Spectator, which published Brock’s story on the Arkansas troopers. Tyrrell stood by that story, saying Brock "was never asked to destroy the Clintons."

But Brock argues that his early experiences have only deepened his commitment.

Many of the researchers who work for him were in diapers during Bill Clinton’s 1992 presidential campaign. But the open floor plan that houses American Bridge’s rapid-response operation is called the "war room," and it is inspired by the hub of Clinton’s campaign, which James Carville helped run out of an old newsroom of The Arkansas Gazette in Little Rock. About 40 staff members are employed as trackers, monitoring candidates in Senate and congressional races across the country. They have tracked a combined 4,443 events and filed more than 900 federal requests for documents so far this election cycle.

Brock said he first had the idea for an opposition research shop to help Hillary Clinton last year, when she testified to a congressional hearing on the 2012 attack on a U.S. Mission in Benghazi, Libya, that left four Americans dead.

This past fall, Brock reached out to another Clinton friend, Burns Strider, who worked on Clinton’s 2008 presidential campaign as a liaison to religious voters, to head Correct the Record.

"I thought: ‘Good Lord, that’s the stress and time commitment of a full-time campaign,’" said Strider, a Mississippi native with a thick drawl. "’Am I ready? Is my family ready?’"

Brock pointed out that America Rising, a conservative political action committee and its Stop Hillary 2016 effort, were already active. "He said we didn’t get the luxury to wait," Strider said.

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