Sen. Richard Blumenthal took to Twitter Friday after the former national security adviser pleaded guilty to lying to the FBI about his conversations with Russia's ambassador to the United States during the transition period before President Donald Trump's inauguration.
Michael Flynn is the first Trump White House official to face criminal charges and admit guilt so far in the wide-ranging election investigation by special counsel Robert Mueller.
Flynn has agreed to cooperate with Mueller's probe, which focuses on Russian meddling in the 2016 election and possible coordination between Russia and Trump's team in the campaign that sent the Republican businessman to the White House.
Flynn could provide Mueller with crucial information about those activities, says Sen. Chris Murphy.
No comment on the plea has yet been made by President Trump or the White House.
AP wires contributed to this report.