Former Vice President Dick Cheney conveyed the message to Vice President Mike Pence over the weekend that he believes portions of the Trump administration's policy resemble that of the previous White House.
Trump himself has not reacted to reports of Cheney's negative judgments.
The clashing opinions on foreign policy and presidential standards reflect a broader schism between hawkish Republicans like Cheney and Trump-era isolationist conservatives.
Cheney, who is no stranger to criticism for his policies during President George W. Bush's presidency, directed his frustration to his Republican successor, who was at the annual World Forum meeting in Sea Island, Georgia, on Saturday. When Cheney referenced news reports indicating that Trump had agreed to pull American troops out of Syria during a phone call with Turkish President Recep Tayyip Erdogan without informing key allies, Pence replied that the move had been under discussion for six months and wasn't "made overnight", according to a source briefed on the conversation.
The former vice president specifically slammed the USA for suspending joint military drills with South Korea and for Trump's alleged intention to make Germany, Japan, and South Korea to pay for the American deployment on the Korean Peninsula, calling it a "New York State real estate [type of] deal".
Cheney reportedly said Trump's stance toward North Atlantic Treaty Organisation, where he has urged countries to stump up more for their defense budgets, "feeds this notion on the part of our allies overseas, especially in North Atlantic Treaty Organisation, that we're not long for that continued relationship, that we're looking eagerly to find ways where somebody else will pick up the tab".
Pence reportedly appeared caught off guard by Cheney's pointed questions.
The former vice president also hammered Trump's habit of announcing major policy decisions on Twitter and undermining intelligence officials.
At one point, Pence, whom attendees described as taken aback by some of the questions, turned to his predecessor and inquisitor and joked, "Man, who wrote all these softball questions?"
Attendees say Cheney was polite and gave Pence plenty of opportunity to respond and defend the Trump administration.
"But we think it's possible to demand that your allies do more to provide for the common defense of all of our nations and, at the same time, reaffirm our strong commitment - whether it be to the transatlantic alliance or to our allies across the Indo-Pacific", he said. The event was marked off the record, but the Post claims to have obtained a transcript.
The reportedly tense discussion showed the divide in the Republican Party over Trump's "America First" approach to foreign policy.
The debate took place during Cheney's interview of Pence for those in attendance.