WASHINGTON — House Democrats are signaling they may quit a Republican-led committee investigating the 2012 Benghazi attacks after Hillary Rodham Clinton endured a grueling interrogation by GOP lawmakers at a marathon congressional hearing.

“We have learned absolutely nothing,” Rep. Adam Smith, D-Wash., a member of the panel, said of Thursday’s contentious 11-hour hearing and the 17-month investigation that preceded it.

Other Democrats, who had labeled the probe a partisan effort to undermine Clinton’s presidential campaign, echoed Smith’s complaint after the former secretary of state finished her testimony. More telling were comments by House Minority Leader Nancy Pelosi, D-Calif., who asked: “What’s next? Is this thing forever? Are they ever going to make a decision about whether to continue this?”

Pelosi has insisted, as she reiterated Thursday, “You have to be in the room to defend the truth.” With Clinton’stestimony concluded, that decision is likely to be revisited. Senior Democratic aides would not rule out the possibility of Democrats boycotting the panel, whose work likely will stretch into the election year.

Rep. Elijah Cummings of Maryland, the committee’s top Democrat,, said no decision has been made on whether Democrats boycott investigation.

Clinton had confrontational exchanges with several GOP lawmakers, but also heard supportive statements from Democrats. The questioning was, by turns, harsh and sympathetic, depending on who was asking.

Clinton firmly defended her record while steadfastly dodging any misstatement or display of anger that might damage her White House prospects. The most combative moments zeroed in on the Obama administration’s shifting initial accounts of the September 2012 attack that cost the lives of Ambassador Chris Stevens and three other Americans. But there were few specific questions about what transpired on that fateful day, Sept. 11, 2012, which Clinton said causes her to still lose sleep to this day.

“I would imagine I’ve thought more about what happened than all of you put together,” she told the committee. “I’ve lost more sleep than all of you put together.”

The panel’s chairman, Rep. Trey Gowdy of South Carolina, said the committee was focused on the facts, not the politics of the situation, in the wake of recent comments by fellow Republicans describing his investigation as an effort to lower Clinton’s poll standings.

Democrats noted that the probe has now cost taxpayers more than $4.5 million and has lasted longer than the 1970s Watergate era investigation.