Joining Sen. Elizabeth Warren's (D., Mass.) team as she stumps across New Hampshire pledging to eliminate corruption from Washington is campaign surrogate Lori Trahan, a first-term Massachusetts congresswoman under investigation for violating campaign finance law.

Warren's plans to battle Washington corruption are central to her 2020 candidacy, making Trahan a potentially problematic surrogate after Office of Congressional Ethics investigators discovered "substantial reason to believe" Trahan committed a violation in 2018. The House Ethics Committee announced in December it would investigate the matter further.

Warren's pitch to voters in New Hampshire and around the country has incorporated battling corruption and side-dealing in Washington that benefits the powerful and well-connected. She also swore off big-dollar fundraising events during the primary and recently pledged not to do them during the general election if she wins the nomination.

"Here’s the good news: I have the biggest anti-corruption plan since Watergate," Warren said at a town hall in Derry last week. "Here’s the bad news: we need the biggest anti-corruption plan since Watergate."

Trahan endorsed Warren at the presidential campaign's outset and has helped with New Hampshire canvassing efforts, joining Sen. Ed Markey (D., Mass.) and other Massachusetts lawmakers backing Warren.

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Trahan faces accusations of skirting campaign finance laws that could have boosted her to a razor-thin margin of victory in her 2018 Democratic primary.

Congressional investigators discovered Trahan's husband David donated $300,000 to Trahan's 2018 campaign. The campaign misreported when the contributions were made to disguise the source of the transactions, the Boston Globe reported.

"On three occasions in 2018, Rep. Trahan may have loaned money to her campaign committee that originated from her husband’s personal funds," the Office of Congressional Ethics said in its December report. "While these loans do not appear to have originated from Rep. Trahan's personal funds, the campaign committee repeatedly reported them as personal loans."

Federal law limited David to giving $5,400 to his wife for the 2017-18 election cycle, although Trahan has argued the $300,000 was hers because it was communal property by virtue of their prenuptial agreement.

The $300,000 represented nearly 12 percent of the $2,557,501 Trahan raised in the race for Massachusetts's Third Congressional District.

The Globe reported a $200,000 deposit from David Trahan into their joint checking account on Aug. 21, 2018, allowed his wife to launch a late advertising blitz ahead of that September's Democratic primary. She edged former Boston City Hall aide Dan Koh in a recount before going on to win the general election.

Koh cried foul after December's report, saying Trahan owed it to the district's voters to make a "full, honest account of her conduct during the election and the consulting clients she claims funded her campaign."

"Congresswoman Trahan has been transparent about this politically motivated complaint since the very beginning, and is fully cooperating with the Ethics Committee's review of the matter," Trahan spokesman Mark McDevitt told the Washington Free Beacon. "She remains confident that when the Committee has the opportunity to review her case, it will be resolved favorably."

The House Ethics Committee has not made a public statement on the investigation since December, and it had no comment when contacted by the Washington Free Beacon.

Warren's campaign did not respond to request for comment.

Meanwhile, another congressional surrogate is causing a headache for Warren for a different reason.

Warren backers are fuming about Rep. Joe Kennedy III (D., Mass.), who has been almost entirely absent from Warren campaign events since introducing the senator at her campaign launch. A scion of one of the country's most famous political families, Kennedy has made only two campaign appearances for Warren over the last year, Politico reported.