Sen. Lindsey Graham, R-S.C., issued a sharp and unusual challenge to the truthfulness of the nation’s top uniformed military commander on Thursday, demanding that U.S. Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, return to Capitol Hill to provide fresh testimony on the Benghazi attacks.

The point of contention involved whether any military officers issued an order to U.S. armed forces personnel on the night of Sept. 11, when the U.S. consulate and a nearby annex came under terrorist attack, to “stand down” from providing assistance.

“I asked [Gen. Dempsey] directly,” Graham said in an exclusive interview with Fox News. “Were there any military assets in motion, to help folks in Benghazi, [that were] told to stand down? And what did [State Department whistleblower] Greg Hicks say? That Lt. Col. [Steve] Gibson -- a DOD employee, a member of the Army -- was in Tripoli, ready and willing to go to Benghazi, preparing to go to Benghazi, and was told to stand down.”

“Clearly,” Graham added, “our chairman of the Joint Chiefs' rendition that no one was told to stand down is now in question.”

What’s more, Graham lumped the chairman into a group of prominent Democrats whom the Senate Republican said he would like to see summoned, or recalled, to the witness chair to testify on Benghazi. These included former Secretary of State Hillary Clinton and Cheryl Mills, Clinton’s former chief of staff.

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The roles of Clinton and Mills occasioned much dispute at Wednesday’s House Oversight Committee hearing where two career State Department employees who consider themselves whistleblowers -- Hicks and Mark Thompson, of the department’s counterterrorism bureau -- offered testimony that pointedly challenged the Obama administration account of the Benghazi attacks.

But the only mentions of Chairman Dempsey on Wednesday were admiring in tone, as Democrats repeatedly cited prior testimony by the general indicating that no military assets could be rallied in time to help the Americans killed in Benghazi.

Then-U.S. Ambassador to Libya Chris Stevens, information officer Sean Smith, and security agents Glen Doherty and Tyrone Woods were killed in two waves of attacks orchestrated, over eight hours’ time on the evening of Sept. 11, by terrorists with links to Al Qaeda. The hearing on Wednesday provided fresh evidence that Obama administration officials knew Benghazi was a terrorist attack “from the get-go,” as Hicks put it, but pressed a false narrative for weeks that depicted the deaths as the result of a spontaneous “protest” over an offensive YouTube video.

Asked to comment on Graham’s challenge to the chairman’s veracity, Pentagon spokesman Maj. Rob Firman told Fox News: “They weren’t told to stand down. They were simply told not to go to Benghazi. They were told to go to the airport in Tripoli to provide security there.”

Lt. Col. Patrick Seiber, a spokesman for the Joint Staff, said separately that Graham could call on Dempsey to testify again, but that the chairman’s remarks “will not change.”

In two exchanges during Dempsey’s appearance before the Senate Armed Services Committee on Feb. 7, Graham elicited testimony about allegations that some military personnel were told to “stand down” in their desire to launch operations to assist the beleaguered Americans in Benghazi.

“Did [then-AFRICOM Commander] General Ham on that night,” Graham asked, “did he order a military asset in motion and someone told him to stand down?” “No,” Dempsey testified.

In calling out Dempsey on Thursday, however, the senator at one point appeared to have recalled his prior interrogation of Dempsey inaccurately. He recalled having asked Dempsey “point blank,” in their exchange in February, where was the closest C-130 plane on the night of Sept. 11.

Graham further recalled that the chairman testified the nearest such plane was in Djibouti, Africa.

But the transcript of the Feb. 7 hearing shows Graham in fact asked the general on that occasion about AC-130 gunships, and that Dempsey never provided any information about the approximate distance between the nearest such planes and Benghazi.

Fox News’ Justin Fishel and Jennifer Griffin contributed to this report.