Democratic leaders like House Intelligence Committee Chairman Adam Schiff, D-Calif., are lying to the public when they continue to spread such assertions, Collins claimed Thursday on "The Story."
"I think that the [Democrats] on the Judiciary Committee... they are just so delusional about what they wanted the Mueller report to say and what it didn't say," he said.
"The collusion and conspiracy -- we put that to rest yesterday. Any Democrat, such as the chairman of Intel, Mr. Schiff, who said, 'there's collusion in plain sight,' -- that's just a false narrative and that's a lie to the American people.
"Mr. Mueller put that to bed."
In addition, the top Republican on the House Judiciary Committee said he believed his Democratic chairman also appears "delusional" about the outcome of the Mueller hearings.
Rep. Jerrold Nadler, D-N.Y. said Thursday the proceedings were a "watershed day in telling the facts to the American people," according to Politico.
To that claim, Collins responded, "I'm not sure he's been through a lot of watershed moments because yesterday was not one that you would put into that category."
He asked Mueller if "conspiracy" and "collusion" were colloquially the same thing, and Mueller said no. Collins then quoted Mueller's own report, which indicated otherwise.
"As defined in legal dictionaries, collusion is largely synonymous with conspiracy as that crime is set forth in the general federal conspiracy statute," Collins read from the report.
Fox News' Ronn Blitzer contributed to this report.