Challenged about his lack of trial experience, Talley said he had previously argued motions in federal district court on behalf of the state of Alabama, often through written briefs rather than in person.
He is one of a handful of Trump's nominees to be rated as "not qualified" by the American Bar Association.
Talley, a lawyer who has never tried a case but has been nominated to a federal judgeship by President Trump, failed to disclose that he is married to a White House lawyer in congressional paperwork, The New York Times reported Monday.
Talley's wife, Ann Donaldson, has reportedly been interviewed by Mueller, which Feinstein says represents "a clear conflict of interest that should have been disclosed".
The White House did not respond to questions about whether the administration sees a potential conflict of interest, and whether Talley should have disclosed that he is married to a White House attorney. The Times reported that Mueller's team recently talked to Donaldson about her notes on conversations with McGahn regarding the firing of former Federal Bureau of Investigation director James Comey.
Feinstein said reports that Donaldson has been interviewed by special counsel Robert S. Mueller III's team as it investigates Russian meddling in the US presidential election show "a clear conflict of interest that should have been disclosed". Mueller was appointed as special counsel after Trump fired Comey earlier this year.
The Judiciary panel approved Talley on a party-line vote last week despite his having received a rare "unqualified" rating by the American Bar Association.
In a statement following The Times story, Democratic Sen.
A spokesman for the Republican-controlled Senate judiciary committee said Talley was not required to list a spouse' occupation on his questionnaire.
"I've already stated my opposition to Brett Talley's nomination to be a federal judge in Alabama", she said. However, the White House, with counsel Don McGahn taking the lead, has been hard at work appointing new federal judges to lifetime positions in an attempt to give the federal courts a conservative makeover.
Talley is one of Trump's most controversial nominees.
Talley, who now serves in the Justice Department's office of legal policy, has never tried a case and has only practiced law for about three years.
The White House has pushed back on the "not qualified" label. She came to the White House in March from Jones, Day Reavis and Pogue, the same law firm where White House Counsel Donald McGahn - Trump's campaign lawyer - formerly worked.
Talley is the fourth of Trump's judicial nominees to receive a "not qualified" rating from the ABA - the second to receive the rating unanimously.