Former Secretary of State Hillary Rodham Clinton laughs as she stands up at the end of her testimony on Capitol Hill. AP Photo/Jacquelyn Martin There was a moment on Thursday when former Secretary of State Hillary Clinton appeared in total control.

She had just finished the second round of four during a marathon, 11-hour grilling on the most controversial point of her tenure at the State Department.

But around 4 p.m. — about six hours after the congressional hearing into the 2012 attack on the US diplomatic mission in Benghazi, Libya, had started — she was all smiles.

"Are you going to come to my Katy Perry concert?" she asked one apparent supporter in the audience, referring to a campaign stop over the weekend in Iowa.

"I hope so!" the man said.

"I hope so, too!" she responded.

Hillary Clinton's summer playing defense has suddenly turned into a fall offensive.

As Dan Pfeiffer, a former senior adviser to President Barack Obama put it, she completed her October "triathlon."

And thanks to a bit of skill and a bit of luck, she's now in her best position in a long time on her quest to succeed Obama in the White House.

In only the past week and a half, she dominated her party's first debate, saw her chief potential rival for the nomination opt against running against her, and drew good reviews for her testimony before Congress while the Republicans who grilled her came out apparently learning nothing.

Clinton, the front-runner for the Democratic presidential nomination, has injected life into her campaign after a virtually lifeless summer.

"All of a sudden," one Democratic operative said, "she looks unbeatable again."

Hillary Clinton walks to the Benghazi hearing. AP Photo/Manuel Balce Ceneta

Not so long ago, Democrats weren't as sure about her as their potential nominee. Since March, she has faced continued questions amid a steady drip of controversy surrounding her use of a private email server as secretary of state. She failed to see many good news cycles since.

It led to what seemed, at times, like longing from many Democrats for a challenge from Vice President Joe Biden. For more than two months, he lingered in the background of the race. Prominent Democratic donors seemed ready to jump on board his ship. Even as a noncandidate, his poll numbers surged, and he fared better in general-election matchups than Clinton.

Biden's presence even hung over the first Democratic debate last week. CNN practically begged him to jump in, making it clear that it was willing to accommodate him attending even if he waited until the day of the debate to announce. The vice president's office released details of his plans for watching the debate, as media speculated about whether he would make a surprise entrance.

Then the debate happened.

Clinton challenged Sanders on gun control, eliciting applause from the crowd. And she got backup from him on the controversy swirling her campaign, when Sanders defended her over her use of a private email server. She was declared the unanimous winner by pundits.

"Hillary Clinton was Beyoncé. She was flawless," CNN Democratic political commentator Van Jones said on the network after the debate.

Vice President Joe Biden and then-Secretary of State Hillary Clinton in 2009. AP Photo/Susan Walsh, File

A narrative quickly cemented: Biden's candidacy had lost its rationale, as a stronger Clinton had emerged from the debate. The evidence quickly followed in polls nationally:

A CNN poll found her up 45-29 over Sanders, a three-point increase from the last CNN survey.

An ABC/Washington Post poll gave her 54% of the vote, up 12 points from last month and a 31-point advantage.

An NBC/Wall Street Journal survey showed her with 49% of the Democratic vote, up seven points from last month and a 20-point lead over Sanders.

A Monmouth University poll found her with 48% of the vote, up six points from last month. She had a 27-point lead over Sanders and a 31-point advantage over Biden.

By Monday, Biden was facing increased pressure to make a decision about entering the race. Despite a posture that suggested he was leaning toward entering the race, he ultimately opted against it with a rather sudden announcement on Wednesday. To many of those close to him, the timing was a surprise. But the ultimate decision wasn't.

"Became clear he wasn't there," a source familiar with Biden's deliberations emailed Business Insider. "So while [I'm] bummed, sure, he made the right decision."

Another person close to the vice president said: "It was clear he wasn't there anymore."

And with help from the House's No. 2 Republican, Majority Leader Kevin McCarthy (R-California), Clinton and her campaign have turned the tables somewhat on the issue that threatened to torpedo her campaign over the summer.

The FBI is still in the middle of an investigation into whether any sensitive material was mishandled in connection to her email account. But Clinton's team has injected a partisan-politics-as-usual frame into the email controversy, after McCarthy suggested last month that the committee had helped drag down Clinton's poll numbers.

"Everybody thought Hillary Clinton was unbeatable, right?" McCarthy told Fox News host Sean Hannity.

"But we put together a Benghazi special committee, a select committee. What are her numbers today? Her numbers are dropping. Why? Because she's untrustable. But no one would have known any of that had happened, had we not fought."

Hillary Clinton at the CNN debate. AP

Clinton and her allies have seized on McCarthy's comments — as well as comments from a Republican member of Congress not on the committee — to argue the committee was created with the sole purpose of damaging Clinton's political standing.

Clinton did so herself on Thursday, when she testified before the committee in a mostly grueling, 11-hour marathon affair. Rep. Adam Schiff (D-California) asked her during one particularly emotional exchange how it felt to be "the subject of an allegation that you deliberately interfered with security that cost the life of a friend."

She took the bait.

"Congressman, it's a very personally painful accusation," Clinton responded. "It has been rejected and disproven by nonpartisan dispassionate investigators. Nevertheless, having it continued to be bandied around is deeply distressing to me. I lost more sleep than all of you put together. I have been racking my brain about what more could have been done."

For their part, even some of Republicans' staunchest advocates said they didn't help their cause. One particularly notable exchange came earlier in the day, when Rep. Mike Pompeo (R-Kansas) grilled Clinton over whether Chris Stevens, the former US ambassador to Libya who died in the Benghazi attack, had been given "access" to her in the same manner as controversial ally and unofficial adviser Sid Blumenthal.

Pompeo asked whether Stevens was given her private email address, phone number, and home address. That prompted Michael McFaul, the former US ambassador to Russia, to tweet a lesson informing people how ambassadors communicate with the secretary of state:

One Democratic strategist quipped to Business Insider that Sanders should request "equal time" from House Republicans to make up for the "gift" they gave to Clinton.

Prominent conservative Erick Erickson, the editor in chief of RedState, called the hearings a "waste of time."

"The hearings are a waste of time because everything about it is politicized and nothing is going to happen," he wrote. "Most of the rest of the committee just wants to grandstand for the folks back home as either prosecutors of or defenders of Hillary Clinton."