(CNN) After two years of searching for problems with the investigation into Donald Trump's campaign advisers in 2016 and their ties to Russia, federal prosecutor John Durham hasn't found wrongdoing by Obama-era intelligence officials involved who were outside of the FBI.
But Durham is still at work, looking at early aspects of the FBI investigation into the campaign. His relatively opaque investigation has now lasted longer than former special counsel Robert Mueller's investigation into Russian interference in the 2016 election and prosecution of dozens of Russians and Trump advisers.
Investigators with Durham's office -- having been delayed by pandemic restrictions last year -- are now arranging witness interviews, according to people familiar with the probe. Grand jury subpoenas also were being used to gather documents in recent months, the sources said.
Durham's probe is focused at least partly on actions by the FBI in its handling of a private intelligence dossier and the bureau's disclosures to the federal intelligence surveillance court, according to people briefed on the matter.
His investigation started in spring 2019 with then-Attorney General William Barr's publicly vague direction to scour intelligence gathering. Now, as Durham putters along, his work is still being watched by the vocally angry ex-President and his supporters. He is now positioned to deliver, at least, a report to Attorney General Merrick Garland that could ultimately be released publicly.
Barr extended Durham's tenure into the Biden administration by appointing him special counsel in October, just before the presidential election, as Trump and Republicans continued to believe a report was imminent. Over the course of last year, Durham had turned his focus toward looking at the leadership of then-CIA Director John Brennan and then-Director of National Intelligence James Clapper, before apparently moving on and continuing to prod the FBI.
While the Barr era at the Justice Department was marked by political drama, Garland is attempting to shift the focus toward civil rights and domestic terrorism prosecutions. Still, Garland pledged at his confirmation hearing he would prioritize speaking with Durham once he became attorney general and would let Durham finish his work.
The Biden administration has said Durham will continue his work as special counsel, but little else. He left his post as Connecticut US attorney last month.
Barr and Trump had openly touted Durham's investigation and the possibility his findings could come before the 2020 election, a prospect the former President claimed would prove he was the victim of a Deep State plot. But by summer, Durham had rejected Barr's push to produce at least a partial report on his findings, according to people briefed on the matter.
Trump's disappointment over Durham was the beginning of a souring in his relationship with Barr, according to former administration officials.
The ex-President revived his grievances as recently as last Friday, issuing a short statement that asked, "Where's Durham? Is he a living, breathing human being? Will there ever be a Durham report?"
Others with ties to Trump also have tried to find a pulse while keeping alive their own anger with the FBI.
Former Trump foreign policy adviser Carter Page - -the target of a FISA warrant in 2016 and 2017 and who was investigated by Mueller and never charged with any crime -- has sued the Justice Department and several former FBI officials, including ex-Director Jim Comey, ex-Deputy Director Andrew McCabe and others in the chain of command that handled the warrant's application or parts of the early Russia investigation. McCabe is a CNN contributor.
Page claims he was unfairly targeted by investigators, and that his privacy was violated, citing Justice Department Inspector General Michael Horowitz's findings of FBI missteps and the Justice Department's own walk-back in the foreign surveillance court of some of the subpoena applications last year. The lawsuit is still in its earliest stage. The FBI and DOJ's initial responses to Page aren't due in court until mid-May.
Barr, in an interview shortly before leaving office, told a Wall Street Journal columnist that Durham's probe hadn't found wrongdoing by the CIA. "The CIA stayed in its lane," he said, adding that includes how the Mueller team conducted its probe.
Durham, as is his style, is keeping his ultimate targets or even lines of inquiry close to the vest.
It's still not clear whether Durham is pursuing additional possible criminal matters following the plea deal and sentencing of low-level FBI attorney Kevin Clinesmith, who pleaded guilty to falsifying information used to support some of the FBI's surveillance applications targeting Page. Clinesmith did not engage in broader cooperation with Durham's investigation, according to his court proceedings -- a telltale sign that other criminal cases could be building.
At least some of the questions on which Durham's investigators have homed in have to do with the way other FBI officials responded to intelligence gathered before the applications to surveil Page, according to people briefed on the matter.
Some witnesses have also been asked about how materials from Christopher Steele, a former British intelligence official who produced a dossier alleging that Trump was compromised by Russian ties, made it to FBI investigators from a law firm working for the Democratic Party, according to a person familiar briefed on the interviews.
That Durham's probe has now lasted longer than the 2017-2019 Mueller probe, which took over the FBI investigation that Durham is now investigating, isn't a surprise to Justice Department veterans. He's known to work methodically and slowly, and rarely speaks, preferring to work away from the spotlight. Even the departure of his top deputy, Nora Dannehy, in the middle of the probe last fall led to little indications about how far it had come and where it was headed.
Dannehy now works for the governor's office in Connecticut and hasn't spoken publicly.