Hillary Clinton testifies on the Benghazi attack before the Senate Foreign Relations Committee on Jan. 23 in Washington. (Linda Davidson/THE WASHINGTON POST)

Republican lawmakers, who have spent months seeking to tie President Obama to last year’s deadly attack on the U.S. diplomatic mission in Benghazi, are increasingly focusing their probe on a new target: former secretary of state Hillary Rodham Clinton.

The GOP-led investigation of the Sept. 11, 2012, assaults that killed U.S. Ambassador J. Christopher Stevens and three others now centers heavily on the State Department and whether officials there deliberately misled the public about the nature of the assault.

Three State Department officials are scheduled to testify before a House committee on Wednesday about the Benghazi attack and its aftermath.

“I think the dam is about to break on Benghazi,” Sen. Lindsey O. Graham (R-S.C.) wrote on his Facebook page Tuesday . . . . We’re going to find people asleep at the switch when it comes to the State Department, including Hillary Clinton.”

On Monday, a Fox News anchor asked Rep. Darrell Issa (R-Calif.) how damaging the issue is for Clinton. “I think it’s damaging because it happened under her watch,” replied Issa, chairman of the House Oversight and Government Reform Committee, which is holding Wednesday’s hearing.

Rep. Trey Gowdy (R-S.C.) says Wednesday’s House Oversight Committee hearing on Benghazi should shed more light on what happened during last September’s attack after months of the Obama administration “deliberately” misleading the public. (The Fold/The Washington Post)

To Democrats, the efforts amount to a baseless and less-than-subtle crusade to tarnish the credentials of Clinton, one of the country’s most popular political figures and the overwhelming favorite for the 2016 Democratic presidential nomination.

“This is the same political exercise as before, with just a different target in mind,” said Rep. Adam B. Schiff (D-Calif.), a senior member of the Select Committee on Intelligence. “They’re no longer going after the White House, perhaps because the president’s not running for reelection, and they’re going after the former secretary of state, perhaps because she will be.”

Frederick Hill, a spokesman for Issa’s committee, denied that partisan politics were involved. “The motivation of the committee is to bring forward information that has been pushed away from the public,” he said.

In an interview Tuesday with CNN, the mother of State Department official Sean Smith, who died in the attacks, said she blames Clinton because “she is in charge. Why wouldn’t she do something about it? I blame her.”

Pat Smith added later about Clinton: “She’s supposed to be on top of it, and yet she claims that she knows nothing, that it wasn’t told to her. Well, who — who is running the place?”

An independent review of the Benghazi assault, led by Adm. Mike Mullen, a former chairman of the Joint Chiefs of Staff, and former ambassador Thomas R. Pickering, found no wrongdoing by Clinton, though critics note that Mullen and Pickering did not interview her.

Clinton also emerged largely unscathed in January when she testified before Congress about Benghazi.

“She was very smart — at some level because she’s been through so many of these kinds of situations in the past — not to say or do anything that was inaccurate or would in any way be inconsistent with the enormous credibility she earned as secretary of state,” Democratic strategist Chris Lehane said. “Because she protected her credibility, their ability to make a bigger issue out of it is very limited.”

But Republican lawmakers, along with Fox News and other conservative media outlets, have kept digging into the complex details surrounding the case. In new testimony revealed this week, for example, U.S. diplomat Gregory Hicks said he sought in vain to get the Pentagon to scramble fighter jets over the diplomatic mission as the attack was underway.

“I have never seen an issue like this where one side is from Mars and the other is from Venus,” said Ari Fleischer, a White House press secretary under President George W. Bush. “Typically on a scandal, people agree it’s a scandal and you don’t have this stark division where one side absolutely sees no evil and the other side sees all evil. This is just bizarre.”

Paul Begala, a former strategist to President Bill Clinton, drew a parallel to the Iran-contra affair of the mid-1980s. “It was one of the biggest scandals of the 20th century and yet it had no impact on Reagan’s vice president’s ability to effectively run for president,” Begala said, referring to George H.W. Bush.

“There’s just no chance that in 31 / 2 years the current demagoguery about Benghazi is going to hurt Hillary if she chooses to run,” Begala continued. “It is absolutely inconceivable.”

In a January Washington Post-ABC News poll, 67 percent of Americans had a favorable impression of Clinton. Among Democrats, 91 percent rated Clinton favorably, including 60 percent who felt “strongly,” according to the poll.

Many of Clinton’s supporters are publicly urging her to run, and a pro-Clinton super PAC, Ready for Hillary, was launched a few months ago. But Clinton has not revealed her intentions. Her husband, the former president, said Tuesday that speculation about a possible candidacy is “the worst expenditure of our time.”

Some Republicans, however, hope that continued scrutiny of Hillary Clinton’s leadership in the immediate aftermath of the Benghazi attack will undermine one of the strongest aspects of her public profile.

“The Benghazi scandal is back!” conservative activist Gary Bauer wrote in an e-mail blast on Monday. Bauer added that he believes that Clinton engaged in a coverup in part because she was “worried about her place in history . . . and her place in 2016!”

In an interview, Bauer said the investigation itself undercuts Clinton’s credibility.

“One of the things she brings to the table is a perception that on foreign policy and defense issues she’s perhaps more serious and experienced than the president has been,” Bauer said. “And I think this would go right to those perceived strengths.”

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