(Reuters) - When Joe Biden was inaugurated as the 46th president of the United States, Marc Elias, watching at home on television, didn't celebrate, at least not exactly.

"I exhaled," he told me with a laugh.

Little wonder.

As quarterback of the Biden campaign's state-level litigation team, the Perkins Coie partner for the last two months worked around the clock to fend off a deluge of election challenges from former President Donald Trump and his allies.

Prior to the election, Elias said, "We knew obviously there was going to be some litigation, but not on the scale we saw." He added, "The volume we saw was unprecedented, and so was the nature of the claims," which if successful would have disenfranchised millions of voters.

While Elias said he never doubted Biden would ultimately prevail, he admits that the stress of handling the cases - especially in the midst of a pandemic - was intense, describing the experience as "emotionally and physically exhausting."

Not only were the stakes enormous, he said, but "most lawyers don't have to litigate with the entire public looking over your shoulder and critiquing your legal strategy."

By Elias' count, he and his colleagues have won 64 cases to date since the election and lost just one, a minor challenge over the deadline (Nov. 9 versus Nov. 12) to confirm the identities of first-time voters who voted by mail in Pennsylvania.

It's an extraordinary record of success. But more than that, the wins have been crucial in shoring up the legitimacy of Biden's election as judge after judge, even those appointed by Trump, tossed suits claiming election improprieties. Some were dismissed for lack of evidence, others for lack of standing. The plaintiffs also withdrew some of the filings.

As then-Senate Majority Leader Mitch McConnell put it in a floor speech on Jan. 6, shortly before rioters overran the Capitol, he "supported the president's right to use the legal system. Dozens of lawsuits received hearings in courtrooms all across our country. But over and over the courts rejected these claims."

Take a bow, team Biden.

A 1993 graduate of Duke University School of Law, Elias has long been a top election lawyer for Democrats.

He was general counsel for John Kerry's presidential campaign in 2004 and lead counsel for Senator Al Franken in 2008, prevailing in the Minnesota senate election recount. He went on to win recount fights for Virginia Attorney General Mark Herring in 2013 and North Carolina Governor Roy Cooper in 2016.

Elias was also general counsel to Hillary Clinton's presidential campaign in 2016. Clinton of course won the popular vote but lost in the Electoral College 227 to 304—roughly the same margin as Biden beat Trump.

Some of the state-level losses for Clinton were squeakers. For example, Trump in 2016 carried Michigan by fewer than 11,000 votes. (Biden, by contrast, beat Trump in Michigan by more than 150,000 votes.)

But the Clinton campaign filed zero lawsuits challenging the outcome of the election.

"No one can accuse me of being resistant to bringing litigation, and the margins in 2016 were closer (than 2020) in some ways," Elias told me. "But we concluded there was not a path there" to victory.

To be sure, he noted, some election results are well worth challenging. Elias points to the 2000 presidential race between George W. Bush and Al Gore, when the outcome of the entire contest hinged on a single state, and when a tiny number of votes (in the end, 537) separated the candidates.

But in 2020? "None of those" circumstances was present, Elias said, still sounding incredulous.

At times, the Trump litigation had the feel of Hercules versus the Hydra - you cut off one head, and two more grew back in its place. In Michigan, for example, Trump and his Republican allies filed nine post-election suits seeking to halt ballot counting or stop the certification of election results, according to Elias' Democracy Docket website, where court filings on both sides are posted.

In Wisconsin and Arizona, there were seven suits, in Nevada, eight, in Georgia 10 and in Pennsylvania, a whopping 15.

For Elias, November and December were a blur. He worked seven days a week, holidays included, from early in the morning until late at night, pausing only for a brief midday break to exercise or "just do nothing," he said, although he avoided watching the news to minimize stress.

One of the most dispiriting moments, he said, was when 17 state attorneys general filed an amicus brief backing Texas' U.S. Supreme Court petition to prevent presidential electors from Michigan, Georgia, Wisconsin and Pennsylvania from casting their votes.

"It was absolutely astonishing," he said. "I never worried about the long-term damage of Trumpism until these 17 AGs signed on to Texas' claim."

Looking ahead four years to the next election, Elias said he worries that Republican legislators will point to unfounded allegations of voter fraud to further restrict voting rights. "But if they do," he said, "they'll see me in court."