Speaking to Major Garrett, chief Washington correspondent for CBS News, the senior Democrat said that it was not just down to the influence of QAnon, but also “a whole range of conspiracy theories orbiting around Donald Trump.”
Mr Schiff, chairman of the House Intelligence Committee, made the comments in conversation with Mr Garrett on the network’s podcast The Takeout.
“Sadly, it has already become essentially a cult, not just of QAnon, but a whole range of conspiracy theories orbiting around Donald Trump,” said the congressman.
“Which of course is a disaster not only for the Republican Party, but is a disaster for the country. We really rely on two functional parties for our system to work, and right now we don’t have that,” he added.
In a damning assessment of the state of the minority party in Congress, Mr Schiff says that Republicans were “entwined” in the falsehoods and conspiracy theories spread by the former president.
“Until they’re able to extricate themselves from this lunatic fringe, until they’re able to extricate themselves also from the person of Donald Trump, there’s not much hope for that party, tragically,” he said.
Mr Schiff made the comments as the House prepared to vote on Thursday to strip committee assignments from Representative Marjorie Taylor Greene of Georgia, the most prominent proponent of wild QAnon-focussed conspiracy theories.
Ms Greene was removed from the committees on which she sat by that vote which saw just eleven GOP representatives in favour of the action.
Mr Schiff slammed Republican leadership for not removing her ahead of a floor vote. He said that having someone on an education committee who had previously denied school shootings took place, made “a mockery of the Congress”.
Ms Green said in a speech on Thursday that comments she had made in videos and on social media posts, including 9/11 denial and being in favour of executing senior Democrats, were “words of the past … [that] do not represent my values”.
Mr Schiff’s comments also come ahead of the second Senate impeachment trial of Mr Trump, which begins on 9 February.
The former president faces one article of impeachment — incitement of insurrection — after falsely claiming to have won the 2020 election by a landslide and encouraging a rally of his supporters to march to the US Capitol and confront lawmakers.
Five people died in the subsequent violent assault on Congress by pro-Trump rioters on 6 January.
In the article of impeachment, House Democrats state that Mr Trump’s actions “foreseeably resulted in lawless action at the Capitol”.
Only ten Republican representatives voted in favour of impeachment and only five GOP senators voted to proceed with the trial in the upper chamber.
Mr Schiff’s prominent role in the Russia investigation and first impeachment of Mr Trump made him a favourite target of the president on social media and during press conferences and at rallies.