"The Senate and the House are net fishing", he added of the congressional investigations into Russia's interference in the 2016 presidential election and possible collusion with Trump's campaign.
It's the latest shake-up for a legal team grappling with unresolved questions on how to protect the president from legal and political jeopardy in Mueller's Russian Federation probe, which is nearing its one-year anniversary.
But there is no indication Trump is now an official suspect in the year-old investigation, or that Mueller has found evidence Trump colluded with the Russians - which the president on Tuesday again denied.
Bottom line: as this CNN reporter says, "Trump's legal team is bracing for the dramatic possibility that Mueller would subpoena the President". He'll be replaced by Emmet Flood a veteran Washington attorney who represented Bill Clinton during his impeachment.
McCarthy said there are strong grounds for executive privilege. The person spoke on condition of anonymity to discuss private conversations.
Caputo and other Trump associates have hired attorneys to deal with the various Russian Federation investigations in Congress and by special counsel Mueller, often at a high price tag.
Still, his retirement is the latest evolution for a legal team marked by turnover. When Dowd quit in March over disagreements with Trump on legal strategy, Jay Sekulow became the lead lawyer on the investigation and is still waiting for his clearance.
But critical decisions lie ahead.
The probe has taken a new turn after the publication of questions Mr Mueller seeks to ask the President, which cover topics including potential obstruction.
Still, the fact that Ivanka Trump has not met with the special counsel's team does stand out considering all the other former and current White House officials who have already been called in. We now know that Mueller picked up the investigation, ran with it and ultimately prosecuted and convicted Flynn.
The New York Times first reported the existence of the list.
However, Dowd did not immediately make clear in what context the possibility of a subpoena was raised or how serious Mueller's prosecutors were about the move.
Mr Trump could bring his own lawyers to a voluntary interview, but not to the grand jury, one possible point of leverage for Mr Mueller in the negotiations.
In response to publication of the questions, Trump wrote on Twitter that "it would be very hard to obstruct justice for a crime that never happened" and that Mueller was investigating a "made up, phony crime".
He says: "What are they afraid of?" That references a tweet Trump posted after reports that Comey described a private dinner with the president in personal memos.
Several Republican House committee chairmen have recently negotiated deals with the Justice Department to turn over documents related to Russian Federation investigations into Trump and also a 2016 investigation into Democrat Hillary Clinton's emails.