Senate Minority Leader Chuck Schumer called on House Speaker Ryan to replace Nunes as chairman of the intelligence committee.
Adding to the swirl of questions was the publication of a series of letters dated March 23 and March 24 involving a lawyer for former Acting Attorney General Sally Yates.
"We believe that the department's position in this regard is overbroad, incorrect, and inconsistent with the department's historical approach to the congressional testimony of current and former officials".
In them, O'Neil pushes back against what he says is Justice Department guidance on what Yates could say about conversations she had with Trump - conversations the department indicated could be covered by executive privilege. The requirement that she not discuss even non-classified material "is particularly untenable given that multiple senior administration officials have publicly described the same events", he said.
Virginia Sen. Mark Warner, the top Democrat on the Senate intelligence committee, said that White House meddling is not helping to "remove the cloud that increasingly is getting darker over the administration". The typically bipartisan panel has been torn by disputes over Nunes' ties to President Donald's Trump's campaign and questions about whether he can lead a probe independent of White House influence.
Ryan said at a press conference Tuesday that there is no need for Nunes to resign or step aside from probe.
Rep. Devin Nunes, R-Calif., asked reporters, "Why would I?" when they asked whether he was stepping down in response to growing calls from some lawmakers.
Ryan responded "no" when asked at a press conference whether he thinks Nunes needs to recuse himself from the House investigation. The person spoke on condition of anonymity to discuss the correspondence.
The White House called the Post story "entirely false" and said the administration had not taken any steps to block Yates from testifying at the hearing at which other Obama administration officials were also scheduled to testify.
O'Neil declined to comment Tuesday, and a Justice Department spokeswoman did not return a message seeking comment.
A lawyer for former deputy attorney general Sally Yates says in letters last week that the Trump administration had moved to squelch her testimony in a hearing about Russian meddling in the presidential election. Flynn was not ousted from the White House until the discrepancies were made public. The panel has no public hearings on its calendar, but Schiff told NPR on Tuesday that Republican and Democratic staffers are continuing to review documents and assemble lists of potential witnesses.
Potential White House entanglement in Congress' investigation of Russian meddling in the 2016 election brought new cries of protest from Democrats on Tuesday as fresh political allegations clouded the probe.
Nunes acknowledged visiting the White House the night before he announced that he had information that some Trump associates may have been snared in incidental intelligence collection before Trump took office on January 20.
House Intelligence Committee's ranking Democrat on Monday called on Nunes, who is chairman of the committee, to recuse himself from the Russian Federation investigation.
That kerfuffle, along with Nunes' decision to cancel this week's hearings, led Schiff to call for Nunes to recuse himself from the Russian Federation investigation.
And had the White House put any pressure on House Intelligence Committee Chairman Devin Nunes to cancel the hearing at which Yates was scheduled to appear? It is very unusual for a committee chairman and ranking member not to coordinate meetings related to an investigation.
Nunes would not name the source of the information, nor would he disclose who invited him on the White House grounds for the meeting.
In the letters, attorney David O'Neil said he understood the Justice Department was invoking "further constraints" on testimony she could provide at a House intelligence committee hearing that had been scheduled for Tuesday.