The hashtag #MoscowMitchMcTreason began trending on Twitter Tuesday morning after Senate Majority Leader Mitch McConnell (R-Ky.) fired back against the nickname "Moscow Mitch" in a fiery speech from the Senate floor.

MSNBC host Joe Scarborough, a former GOP lawmaker, dubbed McConnell "Moscow Mitch" after McConnell on Friday blocked two election security measures.

The hashtag #MoscowMitch quickly began trending on Twitter following Scarborough's comments.

McConnell responded on Monday, decrying the attacks against him as "modern-day McCarthyism."

"I was called unpatriotic, un-American and essentially treasonous by a couple of left-wing pundits on the basis of bold-faced lies. I was accused of aiding and abetting the very man I've singled out as an adversary and opposed for nearly 20 years, Vladimir Putin," McConnell said.

"These pundits are lying, lying when they dismiss the work that has been done. They're lying when they insist I have personally blocked actions which, in fact, I have championed and the Senate has passed," he added. "They are lying when they suggest that either party is against defending our democracy."

Social media users, however, doubled down on their tweets criticizing the senator. Both the hashtags #MoscowMitchMcTreason and #MoscowMitchUnAmericanTraitor began to trend across the United States.

"The Breakfast Club" radio host Charlamagne tha God wrote that it "feels good" to wake up and see the phrase trending nationally.

"These guys are blatantly openly working with the Russians to keep power and until I saw that trending I thought nobody cared. AMERICA your illegitimate president is a Russian agent. #FightTheFascists," he wrote on Twitter.

Grant Stern, an author and podcast host for Occupy Democrats, wrote that it was obvious that Scarborough "struck a nerve" when he coined the nickname.

"When the Senate 'leader' responded, he proved Joe's 100 right by spouting the Kremlin line that investigating Putin's help to Trump is McCarthyism."

Hundreds of other used the hashtags to mock or criticize McConnell, some even picturing him dressed in Soviet-era uniforms.