Rep. Trey Gowdy (R-S.C.) is chairman of the House select committee investigating the Sept. 11, 2012, attacks on a U.S. compound in Benghazi, Libya. (Evan Vucci/AP)

The chairman of the House Select Committee on Benghazi subpoenaed a Pentagon official critical of the investigation, suggesting that he tried to prevent an Air Force sergeant from providing testimony about the night of the 2012 attacks.

“This Pentagon political appointee claimed in an official letter to the committee the Department of Defense could not find a requested witness, despite expending ‘significant resources’ searching for him,” Rep. Trey Gowdy (R-S.C.), the committee chairman, said in a statement Friday. Gowdy was referring to Stephen Hedger, the assistant defense secretary for legislative affairs.

“This witness is still on active duty and confirmed Thursday the Air Force knew exactly who he was — a drone sensor operator who was operating over Benghazi on the night of the attacks,” Gowdy wrote. “Mr. Hedger will now have the opportunity to detail exactly what ‘resources’ he ‘expended’ and how.”

The subpoena comes after Hedger sent Gowdy a letter April 28 that was critical of the investigation and requested a meeting to discuss the use of Pentagon resources in locating witnesses for “multiple and changing” interview requests.

Pentagon spokeswoman Laura Seal said the department “never denied any request of the Committee.”

“We are continuing to work with the Committee on this matter and all of its other requests,” Seal said in an emailed statement.

The back-and-forth over the Air Force witness — known as “John from Iowa” — is expected to raise tensions between the Gowdy and the Defense Department, particularly given Hedger’s prior request for a meeting.

Gowdy spokesman Jamal Ware said the subpoena was issued in the interest of speed.

“Chairman Gowdy wants answers under oath and he wants them quickly — a subpoena accomplishes both,” Ware said Friday in a statement. “The Democrats and administration incessantly whine about the committee’s length, so they shouldn’t be surprised when the committee cuts to the chase.”

Hedger’s complaints about the committee became public after his April 28 letter to Gowdy was reported in the news media.

In the letter, Hedger said the Pentagon “expended significant resources” to locate “John from Iowa” or “anyone who might match the description of this person, to no avail.”

About a month later, on May 20, the Defense Department provided a list of drone personnel that included “John’s” full name, the committee said. He and another drone operator ultimately testified Thursday in closed-door interviews on Capitol Hill.

Ranking Democrat Rep. Elijah E. Cummings (Md.) called the subpoena an “abuse of authority by House Republicans” and a “desperate distraction from a failed investigation.”

“There was absolutely no reason to unilaterally subpoena the legislative staff of the Pentagon — after ignoring their request for a meeting — except to retaliate against the Defense Department for exposing the Select Committee’s abuses, delay this partisan investigation even further into the election season, and distract from the fact that the Republicans have come up empty in their three-year attack on Hillary Clinton,” Cummings said in a statement.

“John” offered “virtually no substantive information we didn’t already have,” Cummings spokesman Paul Bell said in another statement.

Gowdy’s spokesman disputed this characterization. “The operators were able to tell the committee what they were directed to look for, what information they were focused on gathering, what information was relayed up the chain of command and what capabilities the drones possessed,” Ware said in a statement.