Sen. Dianne Feinstein Dianne Emiel FeinsteinFeinstein 'surprised and taken aback' by suggestion she's not up for Supreme Court fight Democrats shoot down talk of expanding Supreme Court Biden leads Trump by 12 points among Catholic voters: poll MORE (D-Calif.) is requesting that acting Attorney General Matthew Whitaker and recently ousted Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE testify before the Senate Judiciary Committee in the wake of the Justice Department shakeup.

Feinstein sent a letter to Sen. Chuck Grassley Charles (Chuck) Ernest GrassleyThe Hill's 12:30 Report: Ginsburg lies in repose Top GOP senators say Hunter Biden's work 'cast a shadow' over Obama Ukraine policy Read: Senate GOP's controversial Biden report MORE (R-Iowa), the chairman of the Judiciary Committee, on Tuesday asking that both men appear before the panel.

Feinstein, in the letter, argued the hearings are necessary to understand why Sessions was ousted last week as attorney general.

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“The circumstances surrounding Attorney General Sessions’ departure raise serious questions, including whether the appointment is lawful and the possible impact on Special Counsel Mueller’s investigation,” Feinstein said in the letter about holding a hearing with Whitaker.

Democrats have separately argued that Whitaker’s appointment violates the department’s line of succession and likely violates the Constitution. Instead, they argue, Deputy Attorney General Rod Rosenstein Rod RosensteinDOJ kept investigators from completing probe of Trump ties to Russia: report Five takeaways from final Senate Intel Russia report FBI officials hid copies of Russia probe documents fearing Trump interference: book MORE was next in line to be acting attorney general and should maintain oversight of special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s investigation into Russian interference in the 2016 presidential election.

Democrats have called on Whitaker to recuse himself from overseeing the investigation, given his previous criticism of the probe.

Feinstein added that a hearing with the acting attorney general is needed to “ensure that he will take no action to restrict or otherwise interfere with the Special Counsel’s work.”

Feinstein added that Sessions should come before the committee to answer questions about former FBI Director James Comey James Brien ComeyDemocrats fear Russia interference could spoil bid to retake Senate Book: FBI sex crimes investigator helped trigger October 2016 public probe of Clinton emails Trump jabs at FBI director over testimony on Russia, antifa MORE’s firing and Russia's election interference.

Republicans have largely brushed off Democratic concerns that Whitaker could interfere with Mueller’s probe.

Though Democrats are weighing how best to respond to the appointment, including a potential lawsuit, they can’t force a Judiciary Committee hearing on their own.

If they want to force Sessions or Whitaker to testify they would need an agreement with Grassley or a majority of the GOP-controlled committee to subpoena them.