Marc Elias served as counsel to both Hillary Clinton’s campaign and the Democratic National Committee in 2016. (David Jolkovski/For The Washington Post)

When Marc Elias, general counsel for Hillary Clinton’s presidential campaign, hired a private research firm in the spring of 2016 to investigate Donald Trump, he drew from funds he was authorized to spend without oversight by campaign officials, according to a spokesperson for his law firm.

The firm hired by Elias, Fusion GPS, produced research that resulted a dossier detailing alleged connections between Trump and Russia. While the funding for the work came from the campaign and the Democratic National Committee, Elias kept the information about the investigation closely held as he advised the campaign on its strategy, according to the spokesperson, who requested anonymity to discuss the internal dynamics.

Elias’s involvement in the financing and internal dissemination of the Trump research underscores the influence he wields behind the scenes in Democratic politics — a role that is now being pushed into the spotlight amid multiple investigations into Russia’s attempts to meddle in the 2016 elections.

The 48-year-old lawyer and his firm, Perkins Coie, represent many of the party’s political committees and candidates. Elias also has worked on behalf of companies such as Facebook, fighting in 2011 to exempt the social media network from disclaimer rules on political ads. The company’s sale of ads to Russian actors during last year’s campaign triggered calls on Capitol Hill for more disclosure of online ads.

Elias’s robust client list — which included both Clinton’s campaign and the Democratic National Committee last year — has led to questions about how he juggles competing interests and whether some of the arrangements create awkward dynamics.

Elias declined to comment.

In September, he accompanied former Clinton campaign chairman John Podesta to a closed-door interview with Senate Intelligence Committee staffers, during which Podesta said he had no knowledge of payments to Fusion GPS, according to CNN.

At the time, it was not publicly known Elias had hired Fusion GPS; that was revealed by The Washington Post this week. Elias, who was there as Podesta's lawyer, did not participate in the interview as a witness, CNN reported.

Podesta did not respond to a request for comment.

While it is common for campaigns to conduct opposition research, Elias’s decision to hire Fusion GPS has drawn intense interest because it resulted in the controversial dossier. Republicans have said their effort to investigate Fusion’s role in producing the dossier will intensify with the revelation that it was funded by Clinton’s campaign and the DNC.

President Trump seized upon the news, saying this week that “this was the Democrats coming up with an excuse for losing the election . . . they made up the whole Russia hoax.”

The dossier was part of research into Trump that Fusion GPS began in the Republican primaries for the Washington Free Beacon, a conservative publication that receives financing from billionaire GOP donor Paul Singer. The Beacon’s role was first reported Friday by the New York Times.

After the Free Beacon stopped funding the project, Fusion GPS founder Glenn Simpson met with Elias at his Washington law office and asked if he was interested, according to people familiar with the arrangement.

Elias agreed, deciding Fusion GPS had more capacity than the campaign's in-house operation to do sophisticated research, according to the Perkins Coie spokesperson. Elias drew from funds that both the Clinton campaign and the DNC were paying Perkins Coie, The Post reported this week.

It is unclear who else was familiar with the arrangement, or who knew that Fusion GPS hired a former British intelligence officer, Christopher Steele, who wrote the dossier. Clinton has not responded to requests for comment.

A spokesman for Rep. Debbie Wasserman Schultz (Fla.), who was DNC chairwoman at the time Perkins Coie contracted with Fusion GPS, said the former chair was “not aware” of the law firm’s arrangement with Fusion.

Elias himself did not receive the dossier but was briefed on some of the information in it, according to his firm's spokes­person. The dossier was published by BuzzFeed after the election.

Clinton campaign officials who said they were not aware of Elias’s arrangement with the firm defended his decision to tap its resources.

“Marc is known as one of the most skilled professionals in Democratic politics, in addition to being the party’s top election lawyer,” said Brian Fallon, who served as a spokesman for the campaign. “I am damn glad he pursued this on behalf of our campaign and only regret more of this material was not verified in time for the voters to learn it before the election.”

Among Perkins Coie's clients is Facebook, which Elias helped in 2011 when the company was asking the Federal Election Commission for an exemption from having to include political disclaimers on the small ads that appear on its site.

Advocates for more transparency of online ads said that better disclosure requirements could have prevented a Russian troll farm from running ads during last year’s election that were aimed at sowing divisions between groups of Americans.

Facebook, which noted that it has pledged to create a system to disclose the ads run on its site, declined to comment on Elias’s role.

Elias is well known in political circles for his work on voting rights cases, an effort that has been funded by Democratic megadonor George Soros. Elias also has scored major victories in hard-fought election recounts, including the 2008 election of Sen. Al Franken (D-Minn.).

His role as the go-to Democratic lawyer in Washington was spotlighted this week when he was slated to testify in the federal bribery trial of one of his clients, Sen. Robert Menendez (D-N.J.). Elias, who had been expected to testify about the advice he gave Menendez about how to fill out financial disclosures, was ultimately stricken from the witness list by the judge.

Even as he has built a robust Democratic client list, Elias has often been at odds with groups that advocate for stricter campaign finance rules, including many on the left, over his efforts that have expanded the influence of wealthy donors in politics.

“He has done good stuff on the voting rights side, but he has also been an opponent of many campaign finance reforms and has been largely responsible for some of the loopholes that exist in the campaign finance laws,” said Lawrence Noble, a former Federal Election Commission general counsel who now works as a senior director at the advocacy group Campaign Legal Center.

Elias played a key role in helping craft a massive expansion of party fundraising that was slipped into a 2014 end-of-the-year spending bill. That measure created new party accounts that can accept donations three times larger than contributions to the general party fund. The Republican National Committee is now using money raised by one of those funds to help pay for the legal bills accrued by President Trump and his eldest son, Donald Trump Jr., in the multiple Russia probes.

In 2015, Elias appeared before the FEC to seek greater interplay between candidates and super PACs, which can collected un­limited contributions. Critics saw it as a way around campaign finance laws that set a strict cap on donations to candidates.

Then-commissioner Ann Ravel, a Democratic appointee, objected to the idea — and was “berated” by Elias, who said she should have raised her concerns earlier, she said in an interview. A key element of the measure passed by a 4-to-2 vote, with Ravel in opposition.

“He was always trying to figure out a way to get around” campaign finance restrictions, Ravel said.

Veteran election law attorney Robert Bauer, who founded the Perkins Coie political practice and recruited Elias, said that anyone practicing political law “cannot escape the politics.”

“It understood that your clients, and their objectives, will come under fire,” Bauer said. “But it is wrong to find fault in a lawyer because he is effective in making the client’s case for a particular law or rule.”

Former secretary of state John F. Kerry, who hired Elias as general counsel for his 2004 presidential campaign, called Elias “an outstanding lawyer.”

“He always gave us advice to live up to the law and not avoid it,” Kerry said.

Former Senate Democratic leader Harry M. Reid, who won a 1998 recount with the help of Elias, said the lawyer’s decision to tap Fusion GPS for research “makes good sense.”

“Time is not on your side in these elections,” Reid said.

Franken, who declined an interview request, praised Elias in a statement for helping him secure his Senate seat, while saying that “I don’t always agree with what he advocates for — including when it comes to campaign finance.”

In his book “Al Franken, Giant of the Senate,” published this year, the senator ribbed Elias about the size of his legal fees, which totaled $3.6 million, according to federal filings. Franken wrote that he was often sequestered at home, “calling people for money to pay our bafflingly large and expensive team of lawyers, led by Democratic super-attorney Marc Elias. (If you’re ever in Washington, check out the Franken Wing of the Perkins Coie law office — it’s gorgeous.)”

Tom Hamburger contributed to this report.