"Despite the baselessness of the charges, I believe it is in the best interests of the House Intelligence Committee and the Congress for me to have Representative Mike Conaway, with assistance from Representatives Trey Gowdy and Tom Rooney, temporarily take charge of the Committee's Russia investigation while the House Ethics Committee looks into this matter," Nunes said in a statement.
He added, "I am requesting to speak to the Ethics Committee at the earliest possible opportunity in order to expedite the dismissal of these false claims."
While Democrats had been calling for Nunes to recuse himself ever since the chairman went to the White House to review intelligence documents showing incidental collection of President Donald Trump aides, the reference to the ethics committee probe was a new wrinkle in an already tumultuous situation in the House.
But what do we know about the ethics investigation so far, and what does it mean for Nunes or the chamber's Russia probe already in progress?
Here's what we know so far:
The ethics committee decided to investigate Nunes
The ethics committee has multiple ways it can open an investigation into a member of Congress -- either through a complaint, a resolution of the House, referral from the Office of Congressional Ethics or a decision by the committee members to investigate one of their colleagues.
Based on the laws cited in the Ethics Committee's public statement, the members of the committee decided on their own to investigate Nunes, citing the panel's investigatory authority over "certain unauthorized disclosures of intelligence."
Nunes blames "several left-wing activist groups" for filing "entirely false and politically motivated" accusations against him, but it's unclear to whom he's referring.
"The Committee is aware of public allegations that Representative Devin Nunes may have made unauthorized disclosures of classified information, in violation of House Rules, law, regulations, or other standards of conduct," said House Ethics Chairwoman Susan Brooks, an Indiana Republican.
She declined to comment further Thursday to reporters.
At least one group -- Citizens for Responsibility and Ethics in Washington -- is championing the decision, saying it had filed a complaint to the Office of Congressional Ethics related to Nunes.
"We requested the Office of Congressional Ethics investigate Nunes for violating House ethics rules by disclosing classified information to the public," CREW communications director Jordan Libowitz said in a statement. "House Ethics decided they don't need to wait for OCE's recommendation, that the potential violation is so grave that they need to investigate right away. We agree."
Republicans fear the precedent set by this investigation
A Republican congressman familiar with the situation told CNN that the ethics committee complaint against Nunes runs the risk of changing the way the intelligence committee does its job.
"Democrats will now be hauled before the ethics committee every time they are suspected of having disclosed classified information," the congressman said. "Nunes and Schiff used to handle these matters privately, whenever a congressman was suspected of having said something he or she shouldn't have. They would walk the member of Congress through and advise them to be more careful. People make mistakes."
Now, the congressman said, with this "bullsh**" ethics committee complaint against Nunes.
"It's going to be a holy war," the congressman said.
Democrats want information from the White House
The ranking Democrat on the House Oversight and Government Reform Committee, Elijah Cummings, called Nunes' decision to step aside "appropriate" but also called on the White House to explain "who was involved in working with him to launder information and spin these conspiracy theories."
In Cummings' statement, he also pointed out that he had sent a letter last week
to White House counsel Donald McGahn and national security adviser H.R. McMaster "asking when they became aware that their own staff members reportedly contacted House Intelligence Committee Chairman Devin Nunes, facilitated his entry into the White House complex, and provided him with access to review classified information."
This is an apparent reference to Nunes secretly visiting the White House to review evidence
that showed incidental collection of intelligence on aides related to Trump's presidential campaign. The day after the visit to the White House grounds, Nunes briefed the press and the President on his findings.
Asked about Nunes' decision to step aside Thursday, a White House spokesman would only say, "This is an internal matter for the House."
We may not learn more for a while
The ethics committee said it won't comment further until it collects more information.
And House members are leaving town for a more-than-two-week Easter recess starting Thursday. That includes Nunes, who was spotted leaving the Capitol Thursday morning.