Washington (CNN) Key Republican senators have called the White House over the past 24 hours to make clear that they expect a fulsome investigation as the FBI reviews allegations against Supreme Court nominee Brett Kavanaugh, CNN has learned.

Following questions about the scope and extent of the FBI investigation, a White House official also told CNN that the White House has made it clear to the FBI that agents are not limited in their expanded background search.

CNN was told that on Friday, Senate Majority Leader Mitch McConnell informed the White House that Republican Sens. Jeff Flake of Arizona, Lisa Murkowski of Alaska and Susan Collins of Maine wanted the FBI to interview four witnesses: Mark Judge, Leland Keyser, Patrick J. Smyth and Deborah Ramirez, the first three possible witnesses to an allegation of sexual assault by Christine Blasey Ford while she and Kavanaugh were in high school. Ramirez has separately accused Kavanaugh in a report from The New Yorker of inappropriate sexual behavior related to his time at Yale. Kavanaugh has denied all allegations against him.

But the senators whose votes hold the key to confirmation wanted the White House to know they expect those interviews to be a start, not necessarily the full extent of the investigation.

Ford, Kavanaugh's first public accuser, has said that Judge, Keyser and Smyth were present at the party where she says Kavanaugh assaulted her in the early 1980s.

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