Secretary of State Hillary Clinton engaged in heated verbal combat with GOP lawmakers over last year's deadly assault on the American consulate in Benghazi, Libya, accepting some of the responsibility for the four U.S. citizens killed, but also blurting out, "What difference, at this point, does it make?" when questioned about the details of the assault.

The nation's top diplomat's long-awaited hearing before Congress was spent defending her role to panels delving into the Sept. 11 attack, which left Ambassador Chris Stevens and three other Americans dead.

Clinton told both the Senate Foreign Relations panel and the House Foreign Affairs Committee, "I take responsibility" for the deaths, but she testified she had no advanced knowledge about the most egregious mistakes associated with it.

Clinton will depart from the State Department in coming days. She'll introduce the nominee to replace her, Sen. John Kerry, D-Mass., to a Senate panel on Thursday. With speculation rampant that she is planning a 2016 presidential run, Clinton fought hard to protect her legacy as secretary of state, telling both the House and Senate that she never viewed the cables from Stevens in Benghazi pleading futilely for additional security in the days before the attack. She noted that more than 1 million cables are addressed to her annually, and she can't review them all.

The former first lady and New York senator put herself at arms length to U.N. Ambassador Susan Rice's subsequent Sunday talk show appearances in which she claimed the attack was a spontaneous response to an anti-Muslim video.

"I called it an attack by heavily armed militants" one day after the killings, she reminded the panels.

Clinton admitted she turned down requests to appear on the talk shows herself and said she did not participate in the Obama administration's decision to send Rice.

"I wasn't involved in the talking points process," she said.

But the administration's initial version of the attack, as described by Rice, was not an intentional fabrication, she said, citing the chaos and contradictions that followed. "There are still ... questions about exactly what caused it, who the attackers were," Clinton told the House panel.

Republicans, particularly Sens. Ron Johnson of Wisconsin, John McCain of Arizona, and Rand Paul of Kentucky, challenged Clinton's defense, with Paul declaring that if he were president, he would have fired her for not reading the cable from Stevens.

"I think it's inexcusable," Paul said.

Clinton told both panels that Congress shares a role in the Benghazi tragedy for not providing enough funding to ensure adequate security, though Republicans argued that the money would not have helped because State Department bureaucrats, who remain on the payroll on administrative leave, had decided there was enough protection for Stevens.

"The tragedy of Benghazi was rooted in bad decisions," said Rep. Ed Royce, R-Calif., who chairs the House panel.

Clinton's most heated exchange occurred in response to Johnson's assertion that the administration "misled" the public about the cause of the attack. Raising her voice, she responded, "Was it because of a protest, or was it because of guys out for a walk one night who decided they'd go kill some Americans? What difference, at this point, does it make? It is our job to figure out what happened and do everything we can to prevent it from ever happening again, senator."

Johnson later told Milwaukee radio station 620 WTMJ that Clinton had used "theatrics" to evade his question. "She didn't want to answer," he said.