Hillary Clinton’s Benghazi moment: her biggest test yet?

Hillary Clinton is having quite a run.

She nailed her debate performance last week, and won a bounce in the polls. Then on Wednesday, the biggest question mark hanging over the 2016 presidential field was resolved. Vice President Joe Biden announced he’s not running, easing Mrs. Clinton’s path to the Democratic nomination.

Next up, the House Select Committee on Benghazi. On Thursday, Clinton sits before the panel to deliver long-awaited testimony on the deadly 2012 attack by Islamic militants on US diplomatic and intelligence facilities in Libya’s second-largest city. She has testified on the Benghazi attack before, early in 2013, in her waning days as secretary of State.

This time, the stakes are much higher. She is running for president, and there’s no room for error. Her manner, analysts say, must be presidential – assertive, not aggressive, straightforward while not appearing defensive.

“Being matter-of-fact is critical,” says Susan MacManus, a political scientist at the University of South Florida in Tampa. “Any perceivable tone that’s overly harsh or overly friendly will be open to criticism. The more matter-of-fact she is, and almost the more boring she is, the better for her.”

Clinton can’t know with certainty what she will be asked. The committee has received a flood of new e-mails, including some written by Ambassador Chris Stevens, who died in the attack. Clinton’s own e-mails from her controversial private server are also fair game, and could form a central line of questioning.

Rep. Trey Gowdy (R) of South Carolina, chair of the House Benghazi committee, says his inquiry has unearthed new information. He is under the gun, too, after members of his own party suggested or stated outright that the investigation is political. His challenge is to prove the worth of his panel’s investigation, the seventh conducted by Congress, in addition to a State Department inquiry.

But it will be Clinton under the klieg lights, a day-long test that requires nerves of steel – all on live television.

She appears to be taking nothing for granted, having dialed back on campaign activities and spent the week preparing. But in a way, she’s had decades of preparation, with more than 30 appearances as a witness before Congress under her belt.

As first lady, Clinton testified on her health-reform plan, and as secretary of State, she appeared routinely. As a senator for eight years, she was on the receiving end of testimony. She can also draw on her experience as a young lawyer advising the House Judiciary Committee during the Watergate scandal.

Her mistakes on the hot seat have been few, but they’re memorable. Most prominent was the moment during her January 2013 testimony before the Senate Foreign Relations Committee on Benghazi, when she grew agitated while speaking of those who perished in the attack, including her friend, Ambassador Stevens.

“The fact is we had four dead Americans,” Clinton said. “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?”

That last line has appeared in countless attack ads against her. And on Thursday, she knows that every word and every facial expression are going out live to the American people, and being recorded for that one sound bite on the evening news – or the next attack ad.

Working in Clinton’s favor is the political circus that has sprung up around her appearance before Congressman Gowdy’s committee. House majority leader Kevin McCarthy’s recent comment linking the committee’s work to a decline in her poll numbers was a pure gift, forever shattering any sense that the panel is above politics.

Another Republican congressman, Richard Hanna of New York, added to the injury when he told a radio host that the panel was “designed” to go after Clinton. A fired Republican staffer on the Benghazi committee fanned the flames when he made the same point.

“A political show, rather than a fact-finding mission, is my expectation” for Thursday’s hearing, says Bruce Buchanan, a political scientist at the University of Texas in Austin.

Gowdy has told Republicans to keep their mouths shut about the panel’s work, and that those who have spoken out don’t know what they’re talking about. Neither McCarthy nor Hanna is a member of the committee. Gowdy has also reportedly tried in vain to get conservative activists to stop fundraising off Benghazi.

It may be that Gowdy’s panel has been hopelessly politicized. That, at least, is the point of Clinton allies, who have filled the runup to her testimony with speeches and ads saying as much.

But that doesn’t mean Clinton can ease up. “She will go in well-prepared, but not overconfident,” says Kristina Horn Sheeler, a professor of communication studies at Indiana University-Purdue University Indianapolis.

And inevitably, Benghazi will be in the public eye until Election Day.

“It’s a serious issue, and it’s one that won’t go away,” says Ms. MacManus. “How each side handles it will be a good get-out-the-vote mobilizer for the other side.

The issue matters far more to Republicans than to Democrats or independents, polls show. Ditto the issue of Clinton’s private e-mail server.

Ultimately, the reality of Thursday’s hearing may not live up to the hype. And if it doesn’t, that’s a win for Clinton. But if it does, if there’s a startling new revelation or if Clinton loses her cool, then her string of good fortune will have run out.