The furor over Comey's firing has put McCabe, the acting director, in a delicate position.
McCabe arrived at the Justice Department in a motorcade Saturday afternoon.
Spicer said Trump's "robust schedule" means that "sometimes we don't get an opportunity to get in to see him and get his full thinking".
Sen. Lindsey Graham, chairman of a judiciary subcommittee investigating Russian Federation, said that Comey should testify before his Senate panel about his discussions with Trump over Flynn, who resigned earlier this year. More candidates are expected to join the pool in the coming days.
So far 14 people - lawmakers, attorneys and law enforcement officials among them - have emerged as candidates.
"'Tapes will be subpoenaed" Perhaps surprisingly, one of the most conservative Republicans in the Senate, Mike Lee of Utah, supported that call, telling a Fox News interviewer that it is "probably inevitable" that any tapes would have to be turned over.
Senior Trump administration officials are due on Saturday to interview four candidates to succeed James Comey as the FBI's permanent director.
That's compared with 38 percent of respondents, including almost two-thirds of Republicans, who agree that firing was due to how Comey handled the investigation into Hillary Clinton's emails. Thompson also served as US attorney for the Northern District of Georgia and held several high-level positions at PepsiCo.
A former New York prosecutor, Garcia has served as an associate judge on the New York Court of Appeals - the state's highest court - since early 2016. James Clapper, the former director of national intelligence, said the Founding Fathers created three co-equal branches of government with checks and balances, but with Trump as president, that was now "eroding".
The New York Times reported the president asked Comey in January to pledge loyalty to him and that Comey refused to do so.
The White House first said this week that Trump made the move because of a negative memo about Comey from the Justice Department, only to have the president later said he made the decision before seeing the memo.
Comey's firing ignited a firestorm in Washington and has prompted speculation over whether Trump's decision hinged on his apparent anger at the FBI's probe into the Trump campaign's potential collusion with Russian Federation during the 2016 election.
The FBI has never had a female director.
The White House initially said Trump was compelled to fire Comey by a critical memo from the deputy attorney general on the director's handling of last year's investigation into Hillary Clinton's email.
John Cornyn, 65, is the number two Republican in the Senate.
One administration staff member, who spoke on condition of anonymity to discuss internal deliberations, admitted that the White House communications staff could have done a better job of smoothing out the administration's message.
Sessions forwarded Rosenstein's memo to Trump and recommended that he remove Comey from his role.
Eight met at the US Justice Department on Saturday [Sunday NZT] with US Attorney General Jeff Sessions and his deputy, Rod Rosenstein.
White-collar defense attorney Alice Fisher has arrived at the Justice Department to interview for Federal Bureau of Investigation director.
It comes as the search intensifies to replace fired FBI Chief James Comey.