Nearly a dozen Democratic senators are calling for an independent special counsel to investigate communications between President Trump’s former national security adviser Michael Flynn and Russia.

The 11 senators sent a letter Tuesday to Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsTrump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status White House officials voted by show of hands on 2018 family separations: report MORE saying that "an independent investigation is now necessary to determine what General Flynn did, who knew about it and when."

“We are deeply concerned about credible allegations that the Trump campaign, transition team, and Administration has colluded with the Russian government, including most recently the events leading to the resignation of Lieutenant General Michael Flynn as National Security Adviser,” they wrote in the letter released Wednesday.

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“To maintain the confidence, credibility and impartiality of the Department of Justice, we urge you to immediately appoint an independent Special Counsel to investigate collusion with the Russian government by General Flynn and other Trump campaign, transition and Administrative officials.”

Wednesday’s letter was signed by Democratic Sens. Richard Blumenthal (Conn.), Tom Udall Thomas (Tom) Stewart UdallOVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' Senate Democrats demand White House fire controversial head of public lands agency OVERNIGHT ENERGY: Trump extends Florida offshore drilling pause, expands it to Georgia, South Carolina | Democrats probe Park Service involvement in GOP convention | Sanders attacks 'corporate welfare' to coal industry included in relief package MORE (N.M.), Tammy Baldwin Tammy Suzanne BaldwinKeep teachers in the classroom Cher raised million for Biden campaign at LGBTQ-themed fundraiser Democrats seek balance in backing protests, condemning violence MORE (Wis.), Tom Carper Thomas (Tom) Richard CarperDemocrat asks for probe of EPA's use of politically appointed lawyers Overnight Energy: Study links coronavirus mortality to air pollution exposure | Low-income, minority households pay more for utilities: report OVERNIGHT ENERGY: Democrats push resolution to battle climate change, sluggish economy and racial injustice | Senators reach compromise on greenhouse gas amendment stalling energy bill | Trump courts Florida voters with offshore drilling moratorium MORE (Del.), Ed Markey Edward (Ed) John MarkeyMassachusetts town clerk resigns after delays to primary vote count Bogeymen of the far left deserve a place in any Biden administration Senate Democrats urge Amazon to recall, stop sales of explosive products MORE (Mass.), Jeff Merkley Jeffrey (Jeff) Alan MerkleyThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Sunday shows - Trump team defends coronavirus response Oregon senator says Trump's blame on 'forest management' for wildfires is 'just a big and devastating lie' MORE (Ore.), Sherrod Brown Sherrod Campbell BrownEmboldened Democrats haggle over 2021 agenda 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 Top Democrats press Trump to sanction Russian individuals over 2020 election interference efforts MORE (Ohio), Dick Durbin Richard (Dick) Joseph DurbinSenate Republicans signal openness to working with Biden Top GOP senator calls for Biden to release list of possible Supreme Court picks GOP ramps up attacks on Democrats over talk of nixing filibuster MORE (Ill.), Chris Van Hollen (Md.), Cory Booker (N.J.) and Patrick Leahy Patrick Joseph LeahyBattle 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 Top Democrats press Trump to sanction Russian individuals over 2020 election interference efforts MORE (Vt.).

The group added that “absent swift action by a Special Counsel, evidence of this troubling conduct will be a high risk of concealment.”

“At stake is the integrity and honesty of our most trusted public officials and the viability of our justice system,” they wrote.

Flynn resigned late Monday amid reports he misled senior White House officials about a series of phone calls with Russian ambassador Sergey Kislyak in December.

The retired Army lieutenant general said in a letter on his resignation Monday that he “inadvertently” gave “incomplete information” to Vice President Pence and others about his discussions with Kislyak.

Flynn's resignation followed reports last week that, despite denials, he and the Russian envoy spoke about U.S. sanctions against Russia before Trump’s Jan. 20 inauguration.

White House press secretary Sean Spicer said Tuesday that Trump asked for Flynn’s resignation once the president’s trust in his adviser "eroded."

Reports emerged later Tuesday that several aides and allies to Trump’s 2016 bid repeatedly conversed with senior Russian intelligence officials, according to intercepted phone calls and phone records.

Current and former U.S. officials told The New York Times they had seen no evidence of collusion in regards to hacking or the 2016 race, or if the talks centered on Trump himself.