WASHINGTON - A senior prosecutor working with Connecticut U.S. Attorney John Durham on his investigation into how U.S. intelligence agencies pursued allegations of Russian interference in the 2016 election has resigned. 

The departure of Nora Dannehy, a well-respected former federal prosecutor in Connecticut who rejoined the government in early 2019 to help Durham with the investigation, is likely to raise fresh questions among Democrats about whether Attorney General William Barr is pushing the case toward a public announcement to benefit President Trump ahead of November's election. They have long accused Barr of having political motives in his decision-making surrounding the Durham probe.

Internal tensions over the pace of Durham's work have grown in recent months, as his investigators have pursued a wide variety of theories, hampered at times by operational limitations due to the coronavirus pandemic, according to a person familiar with the effort. The attorney general and some of those around him have pressed for at least partial results, while Durham's pending workload seemed to stretch for months more, the person said. Such tensions are not altogether surprising; throughout his career, Durham has been viewed by colleagues as a thorough investigator, but one who sometimes took significantly longer than originally expected to finish a case.

With the 2020 election less than two months away, partisan speculation about what Durham will or won't do - and what Barr might say about his work - has intensified.

Republicans are hopeful the prosecutor will bring cases against higher-level Justice Department or FBI officials who worked during the Obama administration, which could validate their critiques of the Russia probe. Democrats, though, fear Barr might orchestrate a late-hour revelation of his findings and alter the presidential race.

Rep. Adam Schiff, D-Calif., chairman of the House Intelligence Committee, tweeted that Barr has been using the Justice Department "as a shield to protect Trump" and go after his enemies. "The Durham investigation was political from the start and issuing 'findings' before the election would violate DOJ policy," Schiff said.

Barr has said the impending election would not delay his releasing Durham's findings, though in a recent interview with NBC News, he declined to say whether there would be any pre-election findings or whether he would issue an interim report.

Barr says he won't wait until after election to reveal Durham's findings. Democrats fear a campaign-altering surprise.

A spokesman for the Connecticut U.S. attorney's office confirmed Dannehy's departure, but declined to comment further. A spokeswoman for Barr referred all questions to the U.S. attorney's office.

Efforts to reach Dannehy were not immediately successful.

The development was first reported Friday by the Hartford Courant, which said she had been considering resignation for weeks.

The paper, citing unidentified colleagues of Dannehy's, said she resigned partly out of concern that the top of the Justice Department was pressuring Durham's team to produce results before the election.

Nick Shapiro, the former deputy chief of staff for ex-CIA Director John Brennan, said Dannehy was "very professional" during Durham's interview with Brennan last month, "and she had been throughout the process." Durham informed Brennan that he was "not a subject or a target of a criminal investigation" but rather "a witness to events that are under review," Shapiro said at the time.

A prosecutor best known for corruption cases, Dannehy has handled politically fraught investigations before. In 2008, then-attorney general Michael Mukasey appointed her to oversee an investigation into the Bush administration's firing of nine U.S. attorneys in 2006. She continued that work into the next, Democratic administration, ultimately concluding that no criminal charges were merited.

In recent years Dannehy has worked for a major defense contractor.

Barr selected Durham in early 2019 to lead an investigation into how U.S. intelligence agencies pursued the Russia-related allegations. Durham, a veteran prosecutor, has taken on similarly sensitive investigations for the Justice Department in the past. Dannehy rejoined him at the Justice Department soon after his appointment.

Last month, a former FBI lawyer pleaded guilty to altering an email that one of his colleagues relied on as he sought court approval to surveil a former Trump campaign adviser during the bureau's investigation of Russia's election interference. The guilty plea marked the first criminal charge to arise out of Durham's work.

As part of his plea, Kevin Clinesmith, who worked in the FBI general counsel's office starting in 2015, told a federal judge he thought at the time he was inserting truthful information, though he conceded he doctored the message.

The allegations against Clinesmith emerged last year, when Justice Department Inspector General Michael Horowitz made reference to them in a report detailing failures in how the bureau applied under the Foreign Intelligence Surveillance Act to monitor former Trump campaign adviser Carter Page as a suspected foreign agent. Page has never been charged with any wrongdoing.

Trump has expressed hope that Durham's work will vindicate his attacks on the Russia probe, and after news of Clinesmith's expected plea became public, the president suggested more allegations may come soon.

"That's just the beginning, I would imagine, because what happened should never happen again," Trump said.

Durham also interviewed Brennan last month, though he has yet to talk to some key, high-level FBI officials involved in the case.

It is unclear what, precisely, Durham is focused on more broadly or whether his findings will implicate more-senior officials. Durham has publicly made known his skepticism of the bureau's cause for opening the Russia investigation, and in questioning witnesses he has shown particular interest in why the bureau pressed ahead with surveilling Page even as authorities found problems with some of the allegations against him.

Durham's investigators have asked in particular about how the bureau handled the case after it came to have doubts about the credibility of Christopher Steele, a former British intelligence officer whose work the FBI relied on in part to obtain the secret court order to surveil Page, people familiar with the matter have said.

Barr has said Durham's first priority is to investigate and charge criminal cases, and the attorney general has said he will not delay the probe's findings because of the looming election. Justice Department policies call for prosecutors to not take actions for the purpose of affecting an election, and by tradition they generally avoid taking steps that could have that appearance.

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The Washington Post's Shane Harris contributed to this report.