Former Congressman Denver Riggleman of West Virginia made the comments during an appearance on CNN.
Mr Riggleman said the party's direction since Donald Trump lost the 2020 election has become increasingly worrying to him.
He pointed out that state Republican parties have embraced conspiracy theories that claim antifa were the actual culprits of the Capitol insurrection and continue to cling to Mr Trump's false narrative that massive voter fraud cost him the election.
"Crazy has started to metastasize at every single level in the GOP," he said. "I'm seeing it here in Virginia. And I'll tell both of you, I was in a town here in central Virginia and saw that there were Trump/Pence signs on the road. Someone had taken a black can of spray paint and painted out Pence's name on some of these signs and put some very nasty words there [that] rhymed with, 'Luck Pence.'"
Speaking with The Washington Post, Mr Riggleman expressed frustration that some members of his party latched onto the spurious voter fraud claims launched by Mr Trump and used them to hawk snake oil to the GOP's base.
He pointed out that conservative "news" sources often feature ads rooted in conspiracy theories; survival buckets for the end of the world, gold investment for the looming dollar collapse, and Republican political donations to help keep all the horrors at bay.
“This is the largest conspiratorial grift in United States history,” Mr Riggleman said. “The grift they monetized eventually became weaponized.”
A less pervasive but perhaps much more potent conspiracy theory embraced by elements of the Republican party is QAnon, a doomsday cult that believes Donald Trump, a rogue government agent with "Q" security clearance and the disguised and still living John F Kennedy Jr are fighting a secret war against Democrats, Republicans not loyal to Trump, and the "deep state," all of whom they believe to be satanic, child trafficking pedophile cannibals.
Mr Riggleman voiced special disdain for that branch of his party, particularly in the person of Rep. Marjorie Taylor Greene, an open supporter of the QAnon movement.
"Not only is it crazy, it is par for the course with Marjorie Taylor Greene," he said. "I have to wonder at this point if there's something mentally there that we have to worry about."
A recent CNN audit of Ms Greene's social media revealed that the Congresswoman has a history of supporting calls for violence against Democratic lawmakers and against federal agents.
In January 2019, Ms Green liked a comment that suggested "a bullet to the head" would be a quicker way of removing House Speaker Nancy Pelosi from office.
She also liked posts calling for the deaths of FBI agents. Many QAnon proponents believe the FBI are part of the deep state and opposed to Mr Trump.
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies