Republican groups that view Hillary ClintonHillary Diane Rodham ClintonGrassley blasts Democrats over unwillingness to probe Clinton GOP lawmakers cite new allegations of political bias in FBI Top intel Dem: Trump Jr. refused to answer questions about Trump Tower discussions with father MORE as the Democrats’ most formidable White House threat in 2016 are pouncing on new controversy about year’s terror attacks in Libya — sensing an opportunity to drag down the former secretary of State’s high approval ratings.

Two powerful GOP outside groups, American Crossroads and the recently formed America Rising PAC, this week released web ads ripping Clinton for the State Department's response to the Sept. 11, 2012 attacks on the U.S. Consulate in Benghazi.

Republicans have been privately nervous for months about the prospect Clinton will run for president in 2016, amid polls showing her leading all potential opponents in both parties.

A late April Gallup poll found 64 percent of American adults had a favorable view of Clinton, while 31 percent held an unfavorable view.

But GOP political strategists say the latest developments on Benghazi raise new questions about her leadership at the time of the attacks, and in their aftermath.

They argue the ongoing congressional investigations into the State Department’s response could damage Clinton’s credibility with voters who did not view her through a political lens during the four years she served as the nation’s top diplomat.

“Looking at her time in State, voters might have this amorphous positive feeling about her time as a diplomat but don't really have any tangible examples of accomplishments to latch onto. Benghazi becomes a major problem for her,” said one Republican political strategist, who spoke to The Hill on background to discuss the politics of the Benghazi fight.

“This is a tangible issue where there are clearly things the State Department did not do well in preparation, and made mistakes in the fallout after. That's something we can really point to as questionable actions of her time at State.”

The American Crossroads and America Rising ads keyed off Wednesday’s congressional testimony from diplomat Gregory Hicks, who was the Deputy Chief of Mission in Libya at the time of the attacks.  

Hicks accused the State Department of lapses and said he’d been demoted for sounding the alarm on a botched response.

"A 22-year-old career diplomatic veteran, intimidated for daring to blow the whistle, all under Hillary Clinton's watch. How could this happen? Why did she blame a video? And was she part of a cover-up?" says the narrator in the Crossroads video.

The America Rising video contrasts clips of Clinton’s congressional hearing in January with Hicks’s own testimony that he immediately believed the Benghazi assault was a terrorist attack rather than a spontaneous protest.

He said that in a conversation with Clinton before UN Ambassador Susan Rice went on television to advance the protest theory, she never mentioned that theory to him.

The America Rising spot said the testimony raises “serious questions raised about Hillary Clinton's leadership.”

Republicans believe that, while voters hold a favorable view of Clinton’s tenure at State, she will be hard pressed to point to a concrete success if she runs for president.

The fact she traveled more extensively than any previous secretary of State would pale in comparison to the Benghazi attack, the Republican strategist said.

“Compare that to 'one million miles flown.’ That's a whole lot amorphous than Benghazi, and this gives us a wedge,” he said.

The outside group ads are only a sliver of the Republican attacks on Clinton.

Five congressional committees are currently investigating the events surrounding Benghazi. Sen. Lindsey GrahamLindsey Olin GrahamGOP and Dems bitterly divided by immigration We are running out of time to protect Dreamers US trade deficit rises on record imports from China MORE (R-S.C.) this week suggested Clinton be compelled by subpoena to testify about some of the latest revelations.

On Friday, ABC News reported the State Department was involved in heavy editing of talking points that the CIA draft about Benghazi attacks, with one official urging the removal of references about the possible involvement of an al Qaeda-affiliated group.

Republican lawmakers have seized on the opportunity to hit Clinton.

Rep. Darrell Issa (R-Calif.), chairman of the House Oversight and Government Reform committee, told CBS that “if Hillary Clinton is not responsible for the before, during and after mistakes ... it's somebody close."

Former Vice President Dick Cheney, during a meeting with Republican lawmakers this week, also urged the GOP to consider issuing a subpoena for Clinton to appear before House panels.

Democrats have cried foul over the hearings, arguing that they are political in nature and that Republicans are interested in hurting Clinton rather than finding out the truth of what happened in Benghazi.

“I hate to see it turned into a pure, prolonged, political process that really doesn’t tell us anything new about the facts,” Secretary of State John KerryJohn Forbes KerryLobbying world Kerry: Trump not pursuing 'smart' or 'clever' plan on North Korea Tillerson will not send high-ranking delegation to India with Ivanka Trump: report MORE said during a Google Hangout on Friday when asked about the hearings.

Clinton supporters argued that the focus on Benghazi was consistent with past GOP efforts to discredit the former first lady and senator.

"Sounds to me like they are taking a page from their 2008 and 2012 playbook and we all know how that turned out. Our grassroots supporters will be ready,” Adam Parkhomenko, executive director of the ‘Ready for Hillary’ super-PAC, said when asked about the outside groups’ videos.

Rep. Elijah Cummings (D-Md.), told MSNBC that Republicans intend “to harm her before she even makes a decision, and then to make sure they've got some material after she decides to run for president, assuming she does,” Cummings said.

In addition to the outside GOP groups, potential Republican presidential opponents to Clinton have entered the fray.

Sen. Rand PaulRandal (Rand) Howard PaulLexington mayor launches bid for Congress Trump-free Kennedy Center Honors avoids politics Meet the Iran hawk who could be Trump's next secretary of State MORE (R-Ky.), who is gearing up for a 2016 presidential run, wrote Friday that the hearings should disqualify Clinton from being president.

"The new evidence we have today — and that continues to mount — suggests that at the very least, Mrs. Clinton should never hold high office again," Paul wrote in an op-ed published in The Washington Times.

Sen. Marco RubioMarco Antonio RubioRyan pledges 'entitlement reform' in 2018 Richard Gere welcomes lawmakers' words of support for Tibet Dem lawmaker gives McConnell's tax reform op-ed a failing grade MORE (R-Fla.), who many expect will also run for president, also penned a Friday op-ed on Benghazi.

The Florida senator wrote the House hearing “raises new questions about Secretary Hillary Clinton's role in the administration's efforts to portray the attack as the result of a spontaneous demonstration, despite abundant evidence to the contrary and efforts by one of her top lieutenants to intimidate those who were asking the right questions.”