Sen. Kamala Harris Kamala HarrisHarris faces pivotal moment with Supreme Court battle Nearly 40 Democratic senators call for climate change questions in debates Joe Biden has long forgotten North Carolina: Today's visit is too late MORE (D-Calif.) on Monday called for the Senate to pass legislation that would protect 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 Russia investigation, a move that comes amid news reports that 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 expects to be fired.

"The Senate must pass legislation to protect special counsel Robert Mueller TODAY," Harris wrote on Twitter.

The Senate must pass legislation to protect special counsel Robert Mueller TODAY. Republican leaders must allow it to be voted on. We can no longer afford to wait. This is a matter of preserving the rule of law. — Kamala Harris (@SenKamalaHarris) September 24, 2018

"Republican leaders must allow it to be voted on. We can no longer afford to wait. This is a matter of preserving the rule of law," she added.

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Multiple news outlets reported Monday morning that Rosenstein, who oversees Mueller's Russia probe, was preparing for his departure as the second-ranking official within the Department of Justice (DOJ).

Axios reported Monday that Rosenstein had verbally offered his resignation to chief of staff John Kelly John Francis KellyMORE. The reported move came just days after The New York Times published an article saying Rosenstein in 2017 proposed surreptitiously recording President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE, and that he discussed with DOJ colleagues the possibility of invoking the 25th Amendment to remove Trump from office.

NBC News on Monday reported that Rosenstein is refusing to resign and that he intends to force Trump to fire him if the president wants him out.

Harris's call for legislative action was echoed by other Democrats, including Sens. Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (N.Y.) and Patrick Leahy Patrick Joseph LeahyDemocrats shoot down talk of expanding Supreme Court Battle over timing complicates Democratic shutdown strategy Hillicon Valley: Russia 'amplifying' concerns around mail-in voting to undermine election | Facebook and Twitter take steps to limit Trump remarks on voting | Facebook to block political ads ahead of election MORE (Vt.).

"It is more urgent than ever that the Senate pass S.2644, the bipartisan bill to protect the independence of the Special Counsel," Leahy said on Twitter. "If we do not defend the rule of law in these moments, we risk losing it."

Democrats have repeatedly called for action on legislation that would protect Mueller's probe.

In April, House Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.) said he didn't think such legislation was "necessary."

Noel Francisco, the solicitor general, would be in charge of overseeing Mueller's investigation if Rosenstein resigns or is fired.