Senate Minority Leader Charles Schumer Chuck SchumerJacobin editor: Primarying Schumer would force him to fight Trump's SCOTUS nominee CNN's Toobin: Democrats are 'wimps' who won't 'have the guts' to add Supreme Court seats Republican senator says plans to confirm justice before election 'completely consistent with the precedent' MORE (D-N.Y.) is warning President Trump not to interfere with special counsel Robert Mueller's Russia investigation after Paul Manafort, Trump's former campaign chairman, was charged as part of the probe.

“The President must not, under any circumstances, interfere with the special counsel’s work in any way. If he does so, Congress must respond swiftly, unequivocally, and in a bipartisan way to ensure that the investigation continues," Schumer said in a statement.

He added that "the rule of law is paramount in America and the investigation must be allowed to proceed unimpeded."

Manafort has been charged with 12 counts including conspiracy against the United States, according to the special counsel's office. Manafort’s former business partner and protegé, Rick Gates, who was ousted from the pro-Trump group America First Policies in April, has also been charged.

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The charges are related to work done by Manafort and Gates on behalf of a pro-Russia political party in Ukraine.

Trump has previously flirted with firing Mueller, sparking bipartisan backlash on Capitol Hill.

Two groups of senators have introduced legislation that would limit Trump's ability to fire Mueller, or have the Justice Department fire him, without a court's approval. And Democrats have warned Trump against trying to pardon individuals caught up in the investigation.

Sen. Mark Warner Mark Robert WarnerIntelligence chief says Congress will get some in-person election security briefings Overnight Defense: Trump hosts Israel, UAE, Bahrain for historic signing l Air Force reveals it secretly built and flew new fighter jet l Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' House approves bill to secure internet-connected federal devices against cyber threats MORE (D-Va.), the top Democrat on the Intelligence Committee, said it is "imperative" after Monday's charges and with the investigation still ongoing that Congress move to protect the "independence of the special counsel."

"Members of Congress ... must also make clear to the president that issuing pardons to any of his associates or to himself would be unacceptable, and result in immediate, bipartisan action by Congress," Warner added.

Sen. Dianne Feinstein Dianne Emiel FeinsteinBiden leads Trump by 12 points among Catholic voters: poll Names to watch as Trump picks Ginsburg replacement on Supreme Court McConnell says Trump nominee to replace Ginsburg will get Senate vote MORE (D-Calif.), the top Democrat on the Judiciary Committee, said on Monday that she would "continue to support Bob Mueller as he follows the facts — his independence must remain sacrosanct."

“I’m also more convinced than ever that both the Judiciary Committee and Intelligence Committee must continue their oversight investigations. Congress must get to the bottom of possible obstruction of justice and collusion as well as Russia’s interference with our democratic institutions," Feinstein added.

In addition to Mueller's investigation, several congressional panels, including the Senate Judiciary and Intelligence committees, are investigating Russia's election interference.

But House Minority Leader Nancy Pelosi (D-Calif.) is doubling down on her months-long push to create an independent, bipartisan panel to lead an investigation into the 2016 election and any potential collusion between Moscow and the Trump campaign.

“Even with an accelerating Special Counsel investigation inside the Justice Department, and investigations inside the Republican Congress, we still need an outside, fully independent investigation to expose Russia’s meddling in our election and the involvement of Trump officials,” she said in a short statement.

House Democrats are pushing legislation, sponsored by Reps. Elijah Cummings Elijah Eugene CummingsBlack GOP candidate accuses Behar of wearing black face in heated interview Overnight Health Care: US won't join global coronavirus vaccine initiative | Federal panel lays out initial priorities for COVID-19 vaccine distribution | NIH panel: 'Insufficient data' to show treatment touted by Trump works House Oversight Democrats to subpoena AbbVie in drug pricing probe MORE (D-Md.) and Eric Swalwell (D-Calif.), that would create a panel consisting of a bipartisan group of outside experts and full-time staff to look into Russia's election interference.

Trump, as well as GOP leadership in both chambers, have been cool to the idea, however, arguing that the ongoing investigations in both chambers are sufficient.

--Mike Lillis contributed to this report, which was updated at 11:31 a.m.