The former FBI director said sending the letter had been the right thing to do.
Instead, they should get to the polls and vote Trump out of office, the former FBI director said.
Representative Jim Jordan previously claimed Hillary Clinton's campaign colluded with Russia in the 2016 presidential election.
The Justice Department inspector general began a review of Comey and McCabe in 2017.
"Donald Trump's presidency threatens much of what is good in this nation," the ex-FBI chief writes.
Blame the Russia investigation, Trump said.
Obama's attorney general gave a rare interview to NBC News.
The 2016 presidential candidate discussed Trump, Putin and Pizzagate with a few hundred young women, many in bright pantsuits, who waited for hours to see Clinton speak.
Republican attitudes toward the law enforcement agency have grown more negative over the past year.
Trump has said the FBI disliked Comey, but the emails suggest otherwise.
The letter, 11 days before the election, has been widely cited as one of the potential reasons Clinton ultimately lost to Trump.