Will Benghazi probe peak at height of Hillary Clinton's 2016 campaign?

As investigation into the deadly Sept. 11, 2012 attack on a U.S. consulate in Benghazi, Libya crawls on, Democrats are starting to sweat that the biggest blemish on Hillary Clinton's record as secretary of state could resurface smack in the middle of the 2016 presidential cycle.

Rep. Trey Gowdy, R-S.C., who's chairing the special committee House Republicans constructed to continue an already lengthy probe into the terrorist strike that left four American diplomats dead, has said he expects the investigation to wrap by the end of 2015, which happens to be prime campaigning season. He told the New York Times the dawdled nature of the investigation isn't politics-driven.

"I promised the family members of the four slain and my colleagues on both sides of the aisle the investigation would be serious and fair," Gowdy said. "Nothing would undercut both of those promises like an orchestrated timing."

Phil Singer, a former Clinton campaign aide, argued otherwise: "If it walks like a duck and quacks like a duck, it probably is a duck," he told the Times. "It's hard to look at the timing and think it's simply a coincidence that it would wrap up in the heart of the presidential campaign."

Democrats have called the new panel itself redundant, given that there have been seven separate committee investigations into Benghazi already. Maryland Rep. Elijah Cummings, the panel's top Democrat, told the Times: "The question now is what is left to investigate, and I do not think we need until 2016 to answer it."

In the forefront of the inevitable thorn in Clinton's side is some damning testimony in prior hearings from State Department officials. For instance, Gregory Hicks, the second-ranked diplomat at the U.S. Embassy in Tripoli, testified that his requests to deploy additional military resources in Benghazi to address heightened security issues were repeatedly denied.

Should the investigation lurch on through next year, it does stand to pose some serious cleanup for Clinton, who's been manning the frontline of Democrats' top-billed picks to succeed Mr. Obama for years.

Republicans have been building their case for months: Former Vice President Dick Cheney speculated in May that Clinton "clearly bears responsibility for whatever the State Department did or didn't do" in Benghazi. He also prophesized it would be "a major issue" for a future White House bid.

The wildly varying accounts of how administration officials reacted in the wake of the strike also provided some fodder.

As early as May 2013, the Karl Rove-founded "super PAC" American Crossroads ran a paid attack ad accusing Clinton of orchestrating a "cover-up." that prompted then-United Nations Amb. Susan Rice to unsuccessfully try to promote the case that it began "spontaneously out of protests in Egypt." House Oversight and Government Reform Committee Chairman Darrell Issa, R-Calif., also posited there's "no question" someone from Clinton's circle had a hand in the bumbled response.

"If Hillary Clinton is not responsible for the before, during and after mistakes... it's somebody close," Issa told CBS News. "There certainly are plenty of people close to the former secretary who knew, and apparently were part of the problem."

For her part, Clinton has admitted responsibility for the tragedy, and has called it the "biggest regret" of her tenure at the State Department.