"…it became clear to me that I could no longer be associated with the Republican Party [and] that leadership does not stand up and say the process, the election is over,” Mitchell said during an exclusive interview with CNN Monday.
Mitchell said he voted for Trump in the 2020 election and is a conservative - voting with Republicans 95% of the time - but that Republicans "must stand up for democracy first, for our Constitution first, and not political considerations, not simply for raw political power."
"This election simply confirms for me it's about power first and that, frankly, is disgusting and demoralizing," Mitchell said.
"Losing is brutal, it's personal and it hurts. But if you're not willing to accept that, you should not be in political leadership," Mitchell said.
Mitchell's comments come as electors met across the U.S. on Monday to formally elect Democratic nominee Joe Biden as the president-elect based on the outcome of the Nov. 3 election.
Mitchell said he's been critical on some of the administration's positions in recent weeks and months because it is his duty to stand up and do the right thing based on his principles.
"It's why I'm ending my tenure in Congress by speaking out, in this case, that our leadership owes us better than what we are seeing right now and until I see that, I'm going to be an independent because it's simply unacceptable," he said.
With his decision, he becomes the second Republican member of Michigan's current congressional delegation to abandon the party.
Mitchell is following in the footsteps of fellow Michigander Rep. Justin Amash, who left the GOP in the summer of 2019 and is now a Libertarian.
Mitchell said he notified GOP leaders in a letter that he is withdrawing his "engagement and association with the Republican Party at both the national and state level."
In a letter sent to House Republican Minority Leader Kevin McCarthy and Republican National Committee Chairwoman Ronna McDaniel, Mitchell said It is "unacceptable for political candidates to treat our election system as though we are a third-world nation and incite distrust of something so basic as the sanctity of our vote."
"Steps must be taken, by each state, to audit election results, validate ballots and process and report findings to ensure that every legal vote counts," he said in the letter. "However, the president and his legal team have failed to provide substantive evidence of fraud or administrative failure on a scale large enough to impact the outcome of the election."
"Ronna, you know Michigan politics well. President Trump did not lose Michigan because of Wayne County, but rather he lost because of dwindling support in areas including Kent and Oakland County, both previous Republican strongholds," Mitchell continued.
Mitchell also noted that Republican leaders had been collectively sitting back and tolerating "unfounded conspiracy theories and 'stop the steal' rallies without speaking out for our electoral process.”
"…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,” Mitchell said in his letter.
Mitchell had been open about his criticisms with Trump in recent weeks.
"Oh my God," Mitchell tweeted last month, "@realDonaldTrump Please for the sake of our Nation please drop these arguments without evidence or factual basis. #stopthestupid."