Former Defense Secretary Leon Panetta testified to the House Benghazi committee Friday -- his first appearance before the panel set up to probe the 2012 terrorist attack.

Panetta’s interview with the Republican-led panel was behind closed doors. It was expected to focus on the timeline on the night of the attack, and whether the State Department or White House held up clearance for military assets to intervene.

While the testimony was Panetta's first to the committee, he told Congress in 2013 that time, distance and the lack of an adequate warning prevented a quicker response to the Sept. 11, 2012 attacks that killed U.S. Ambassador Chris Steven and three other Americans.

Panetta told MSNBC this week that "there was never any order to stand down. On the contrary, the whole effort was to do everything possible to try to save lives."

Panetta’s appearance came just a day after he formally endorsed Hillary Clinton, secretary of state during the attack, for president.

The Republican staff on the committee issued a statement on Friday defending the panel's work and criticizing Democratic members, underscoring how Benghazi remains a politically charged issue more than three years after the attacks.

Democrats in turn blasted the committee, saying Republicans were “trying to clean up their mess” after Clinton’s appearance in October.

“The Republicans said they wanted to talk to Secretary Panetta back in 2014, but they abandoned their own plans last year when they decided to use the Select Committee to try to derail Hillary Clinton’s presidential campaign,” said Ranking Member Elijah Cummings, D-Md.

“The problem is that even Republicans condemned their marathon hearing with Secretary Clinton as an epic failure, so now they are trying to clean up their mess,” Cummings said.

Panetta’s appearance comes just two days after former CIA Director David Petraeus was interviewed by the panel, spending four hours behind closed doors‎. Democrats said that Petraeus’ testimony was consistent with what he’d said in the past, and with the conclusions of a bipartisan House intelligence committee report.

The report, issued in November 2014, said there was no intelligence failure, no delay in sending a CIA rescue team and no missed opportunity for a military rescue.

Rep. Adam Schiff, D-Calif., said he hoped "this is the last time we have to bring the director back to repeat his testimony." But Rep. Trey Gowdy, R-S.C., the panel's chairman, said he expects to call Petraeus to testify again because several committee members did not question the retired Army general.

"We're actually not through with him," Gowdy said.

The 12-member committee has spent more than $5 million since its creation in May 2014.

Democrats say the inquiry has gone on longer than the 9/11 Commission took to investigate the terrorist attacks that killed nearly 3,000 people on Sept. 11, 2001.

Fox News’ Catherine Herridge and The Associated Press contributed to this report.