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 Mrs. Clinton says it is far too early for her to consider a run for the presidency, a sprawling and well-funded operation built by Mr. Brock has already established a rapid-response nerve center for her.
Mr. Brock is determined to defend and define Mrs. 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, Mr. 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’s 1994 sexual harassment lawsuit against Mr. Clinton and Mr. Brock’s elevation in Republican power circles.
On Tuesday, Mr. Brock will return to Arkansas for the first time since that article, this time in the warm embrace of the Clinton world: He is a featured speaker at the Clinton School of Public Service at the University of Arkansas, delivering an address titled “Countering the Culture of Clinton Hating.”
The Clintons have no official role in Mr. 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.
The “super PAC” he founded, American Bridge, has tapped into the rich network of Clinton supporters, like George Soros; Steve Bing; Stephen M. Silberstein, a Bay Area entrepreneur; and Susie Tompkins Buell, a friend of Mrs. Clinton’s based in San Francisco, according to federal disclosures.
Mr. Brock 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, Mr. Brock has started a new initiative within it, called Correct the Record, to focus exclusively on 2016 and defending Mrs. Clinton.
Combined, Mr. Brock’s organizations brought in $25 million in donations last year, he said.
Mr. Brock has apologized publicly for his early attacks on the Clintons, suggesting he was a naïve young conservative pressured by the movement’s leadership to participate in what he calls the politics of personal destruction. But people close to Mr. Brock have said his ultimate act of penance would be to help get Mrs. 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 fund-raising vehicle devoted to a Clinton candidacy.
The speech on Tuesday signals a full-circle evolution for the man whose answering machine during the mid-1990s said, “I’m out trying to bring down the president.” He said the address would grapple with the question of whether there has been a resurgence of “the kind of anti-Clinton animus that was motivating a lot of the conversation in the 1990s.” He asked, “Is there a vast right-wing conspiracy redux?”
Not everyone, of course, views Mr. Brock as trustworthy; some conservatives called him a “switch-hitter” who employs the same tactics he once used against the Clintons against their enemies. But he argues his early experiences have only deepened his commitment.
“In the early and mid-’90s, I was on a mission to try and bring the Clintons down, essentially, and now I’m coming back 15 years later with a very different perspective — not only as somebody who’s supportive but somebody who is actually doing some work in relation to her potential presidential candidacy,” Mr. Brock said.
In 1996, Mr. Brock wrote a flattering biography of the first lady and, later, publicly changed his political affiliation. His 2002 book, “Blinded by the Right: The Conscience of an Ex-Conservative,” provided a firsthand account of his evolution and resonated with the former president. Mr. Clinton was known to hand out copies of Mr. Brock’s book as proof that the “vast right-wing conspiracy” (a term Mrs. Clinton used in a 1998 television interview) existed.
Mr. Brock declined to discuss his relationship with the Clintons, but, according to several accounts, he is a friend and adviser who is in contact with Mrs. Clinton and former White House advisers like Maggie Williams, who helped Mr. Brock start Media Matters, and Sidney Blumenthal, the New Yorker writer turned Clinton aide.
Last year, Mr. Clinton delivered the keynote address at a fund-raiser in New York for Mr. Brock’s biggest donors. Mr. Brock thanked the former president and Mrs. Clinton for “giving me the gift of forgiveness,” said one person who attended the fund-raiser but could not discuss the event, which was closed to the news media, for attribution.
These days, at age 51, Mr. 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.
Many of the researchers who work for him were in diapers during Mr. 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 Mr. 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.
Mr. Brock said he first had the idea for an opposition research shop to help Mrs. Clinton last year, when she testified to a congressional hearing on the 2012 attack on a United States Mission in Benghazi, Libya, that left four Americans dead.
“Secretary Clinton held no political office and had no political staff, and that was hampering a response to a lot of the false allegations that were coming out of the Benghazi hearings,” Mr. Brock said. “It didn’t seem to be anybody’s job to respond to that in real time.”
In October, he published an e-book called “The Benghazi Hoax,” which defends Mrs. Clinton’s handling of the attack. And through his media appearances and behind-the-scenes interactions with reporters, he helped discredit an Oct. 27 report on CBS’s “60 Minutes” that led to the network’s apology and the journalist Lara Logan’s leave of absence.
The takedown of the CBS report is exactly the type of response Mr. Brock hopes Correct the Record can do in real time as attacks on Mrs. Clinton intensify.
This past fall, Mr. Brock reached out to another Clinton friend, Burns Strider, who worked on Mrs. Clinton’s 2008 presidential campaign as a liaison to religious communities, to head Correct the Record.
“I thought: ’Good Lord, that’s the stress and time commitment of a full-time campaign,” said Mr. Strider, a Mississippi native with a thick drawl. “ ‘Am I ready? Is my family ready?’ ”
Mr. 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,” Mr. Strider said.