READ: House Republican's letter leaving the GOP

Rep. Paul MitchellPaul MitchellFormer Rep. Paul Mitchell announces renal cancer diagnosis Unnamed law enforcement banned under the new NDAA Growing number of House Republicans warm to proxy voting MORE (R-Mich.) on Monday told Republican leadership in a letter that he is leaving the party.

In the letter, which Mitchell shared on Twitter, the retiring lawmaker cited President TrumpDonald TrumpMeghan McCain: Democrats 'should give a little credit' to Trump for COVID-19 vaccine Trump testing czar warns lockdowns may be on table if people don't get vaccinated Overnight Health Care: CDC details Massachusetts outbreak that sparked mask update | White House says national vaccine mandate 'not under consideration at this time' MORE's efforts to dispute the presidential election.

"If Republican leaders collectively sit back and tolerate unfounded conspiracy theories and 'stop the steal' rallies without speaking out for our electoral process, which the Department of Homeland Security said was 'the most secure in American history,' our nation will be damaged," he wrote.

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"I have spoken out clearly and forcefully in opposition to these messages. However, with the leadership of the Republican Party and our Republican Conference in the House actively participating in at least some of those efforts, I fear long-term harm to our democracy," he added.

Read the full letter below.