Sen. Claire McCaskill Claire Conner McCaskillDemocratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally Missouri county issues travel advisory for Lake of the Ozarks after Memorial Day parties MORE (D-Mo.) is demanding that 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 resign over reports that he spoke with Russian Ambassador Sergey Kislyak during the presidential campaign, then denied any meetings under oath during his confirmation hearing.

"A good prosecutor would have known these facts were relevant to the questions asked,” McCaskill said in a statement on Thursday morning. “It’s clear Attorney General Sessions misled the Senate—the question is, why?"

She added that the former GOP senator "should resign."

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Sessions did not disclose those conversations during his confirmation hearings for attorney general, testifying under oath that he “did not have communications with the Russians."

McCaskill added that as a member of the Senate Armed Services Committee, which Sessions also served on as a GOP senator from Alabama, she's never been contacted by the Russian ambassador.

"I’ve been on the Senate Armed Services Committee for 10 years, and in that time, have had no call from, or meeting with, the Russian ambassador. Ever," she said. "That’s because ambassadors call members of Foreign Relations Committee."

ADVERTISEMENT Sessions reportedly spoke with Kislyak during a July Heritage Foundation event at the Republican National Convention attended by about 50 ambassadors. A Department of Justice official told The Washington Post Kislyak was among a group of diplomats who approached Sessions and spoke with him informally there. Sessions also spoke with Kislyak via phone in September, according to a spokeswoman for the attorney general. The conversation took place during a time when U.S. intelligence officials assert that Russia was interfering in the 2016 race through a hacking and influence campaign intended to help sway the election for President Trump.

Sessions told NBC News on Thursday that he did not talk about "any political campaigns" with Russian officials, but opened the door to recusing himself from a Russia probe.