US Rep Peter Meijer, who has spoke out in the past against the conspiracy theory, made the comments during an appearance on CNN.
"The fact that a significant plurality, if not potentially a majority, of our voters have been deceived into this creation of an alternate reality could very well be an existential threat to the party," Mr Meijer said.
The QAnon conspiracy arose from the 4chan and 8chan image boards and alleges that a rogue intelligence agent with a "Q" level security clearance was working with Donald Trump to fight the "deep state" that actually controls the government and is made up of Satanic, cannibal sex trafficking pedophiles. The "deep state" includes members of the media, Hollywood celebrities, Democratic lawmakers and operatives, some insufficiently conservative lawmakers, and generally anyone else who opposed Mr Trump.
The conspiracy theorists looked forward to an event called "the storm" in which they believed Mr Trump would round up the deep state members and either jail or execute them.
US Rep Marjorie Taylor Greene previously supported the QAnon conspiracy movement, and has since claimed she no longer buys into the theory. US Rep. Lauren Boebert also said she "hopes it's true" that someone was fighting against the "deep state."
Even Mr Trump never outright denounced QAnon, and usually feigned ignorance on the subject when asked.
While not all QAnon adherents believe fully in the theory, Mr Meijer believes it has infected the thinking of many Republican voters, causing them to lose faith in mainstream information, whether coming from conservative or liberal leaning sources.
"When we say QAnon, you have the sort of extreme forms, but you also just have this softer, gradual undermining of any shared, collective sense of truth," Mr Meijer said.
He said that the impossible expectations built by the conspiracy could lead to "a cycle of disillusionment and alienation" among Republicans, which could eventually drive them to drop out of electoral politics altogether or engage in more violent attacks like the one at the Capitol on 6 January.
Mr Meijer is not the only Republican lawmaker speaking out against the theory.
US Rep. Adam Kinzinger has also denounced QAnon, telling CNN that the conspiracy could fuel further violence.
"Do I think there's going to be a civil war? No. Do I rule it out? No. Do I think it's a concern, do I think it's something we have to be worried about? Yeah," he said.
A recent HBO documentary, "Q: Into the Storm" explores the rise of the conspiracy theory and its impact on American culture.
The series' finale builds an argument implicating Ron Watkins, who runs the 8chan image board, as being the individual behind the "Q" posts that fuels the movement.
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