The administration had initially claimed the Sept. 11 attack on the U.S. Consulate in Benghazi was sparked by an anti-Islam video made in the United States. Later, officials changed their story, saying the attack was an act of terrorism linked to al Qaeda. 

Four Americans, including U.S. Ambassador to Libya Christopher Stevens, were killed in the assault. 

Republicans have hammered Obama over the episode, arguing that it's evidence of a failed foreign policy strategy — a notion Biden rejected Thursday.

“The intelligence community told us that [the video sparked that attack],” Biden said. “As they learned more facts about exactly what happened, they changed their assessment.”

Republicans aren't buying it, arguing that it was clear from the start that the well-armed attackers were not merely protesters who turned violent.

“It took the president two weeks to acknowledge this was a terrorist attack,” Rep. Paul RyanPaul Davis RyanRepublicans are avoiding gun talks as election looms The Hill's 12:30 Report Flake to try to force vote on DACA stopgap plan MORE (R-Wis.), said during Thursday night's debate. “He went to the U.N. and in his speech at the U.N. [on Sept. 25] six times talked about the YouTube video." 

Republicans have also accused the administration of failing to provide enough security in Benghazi. 

Behind Rep. Darrell Issa (R-Calif.), Republicans on the House Oversight and Government Reform Committee staged a hearing Wednesday where two Libya-based security officers said the State Department rejected their requests for more protection.

“The takeaway … for me and my staff, was abundantly clear — we were not going to get resources until the aftermath of an incident,” Eric Nordstorm, regional security officer for the State Department, testified.

Biden on Thursday denied knowledge of such requests.

"Well, we weren’t told they wanted more security there," Biden said. "We did not know they wanted more security."

The tragedy has thrust foreign policy to the front of an election debate that was expected to focus on the economy, while putting Obama on the defensive over an issue his team had thought was untouchable after the killing of Osama bin Laden.

McGovern on Friday dismissed Issa's Oversight hearing as a "show trial" conducted to score political points ahead of the elections.

"Unfortunately, we have a bunch of show horses here in the House who don't want to wait for an investigation to be completed before they make their judgments, but the right thing to do here is to let the investigation go forward," he said. 

"If there were mistakes made, let's identify them and make sure they never happen again. But let's deal with facts and not make this into a political football."

McGovern also went after Ryan's budget proposal, which cuts discretionary spending — including the State Department budget — by 19 percent across the board in 2014. 

Democrats say that plan would lead to a $300 million cut in embassy benefits, including security. 

"The Republicans are talking about security for our diplomats overseas and Paul Ryan has a budget that would decimate the funding for security for our diplomats overseas," McGovern said.

Republicans counter that the Ryan budget doesn't specify cuts to embassy security, but instead leaves it to appropriators to decide where the cuts would fall.