CIA Director Mike Pompeo, President Trump's nominee to replace Rex Tillerson as secretary of state, has reached out to Hillary Clinton for advice as he prepares for an arduous Senate confirmation process, according to a report.

In addition to receiving State Department briefings and taking part in mock question-and-answer sessions, Pompeo has had "lengthy calls" with former living chief diplomats such as Clinton and John Kerry, per Politico.

“He understands the gravity of the challenge before him,” a source told the news outlet.

The outreach effort marks a pivot for Pompeo's relationship with Clinton, whom he grilled for her response to the deadly 2012 attack in Benghazi, Libya, when he was a member of the House.

In their calls, Clinton emphasized the importance of encouraging career diplomats to stay in the foreign service following several resignations under Tillerson's tenure, Politico also reported.

Last week, Clinton said she saw Trump's nomination of Pompeo as a "‘small glimmer of hope" given his successful leadership of the CIA.

“I view it as a national security threat that the State Department has been so decimated, and I don’t know what will happen with the nomination of Mike Pompeo to become the next secretary of state, but the one small glimmer of hope is when he went into the CIA, he only brought two people with him and he really relied on the career intelligence people,” Clinton said.

Pompeo's confirmation hearing before the Senate Foreign Relations Committee is set for Thursday.