Hillary Clinton’s aggressive approach of late is aimed in part at answering one of Democratic activists’ regular complaints about her: that despite posturing as a fighter, she has rarely taken the gloves off. (Mario Anzuoni/Reuters)

After months of remaining largely above the partisan fray — and often appearing cautious to a fault — Hillary Rodham Clinton has begun taking more risks and landing some punches against Republicans.

The more aggressive posture comes as Clinton has suffered an erosion in her public image, with more potential voters saying they view her unfavorably than at any point since she entered the 2016 race and fewer people saying they find her trustworthy.

That trajectory and the drumbeat of news about Clinton’s unorthodox e-mail system when she was secretary of state have frayed some Democratic nerves and have fueled speculation that Vice President Biden may see a path to challenge the long- ­dominant candidate.

It also comes as her biggest rival for the Democratic nomination, Sen. Bernie Sanders (I-Vt.), is drawing crowds of 10,000 or more in the country’s most liberal bastions — underscoring Clinton’s enduring weakness within the party’s progressive base.

Clinton’s stepped-up tempo has included almost daily attacks on the better-known contenders among the wide Republican field, particularly billionaire front-runner Donald Trump and former Florida governor Jeb Bush.

“Republicans are systematically . . . trying to stop millions of American citizens from voting,” Clinton wrote in a Twitter message Thursday typical of her recent postings. “What part of democracy are they afraid of?”

The Clinton campaign also made a surprise release of her health and tax information late last month on the same day as a very public airing — in the home state of Bush and Sen. Marco Rubio (R-Fla.) — of her policy reversal on U.S. relations with Cuba.

The Clinton team mounted a preemptive spin campaign ahead of last week’s maiden Republican debate and then invited reporters covering her to watch the two-hour debate at Clinton’s Brooklyn headquarters.

“They’re all so out of touch, it’s hard to choose” a favorite among the 10 Republicans on the debate stage, Clinton campaign manager Robby Mook joked partway through the event.

The week before, Clinton caught Bush off guard with a strong denunciation of his positions on Medicare, the Affordable Care Act and voting rights as he waited offstage to address the same civil rights forum. In the following days, she critiqued Trump, Wisconsin Gov. Scott Walker and former Texas governor Rick Perry by name.

That elbows-out approach was out of character for the careful, no-false-moves operation Clinton has built as the Democratic front-runner. The strategy is aimed in part at answering one of Democratic activists’ regular complaints about Clinton: that despite posturing as a fighter, she has rarely taken the gloves off.

“It’s one thing to say it and another to really do it,” said Scott McLean, a professor of political science at Quinnipiac University, whose national poll is among those that have charted the erosion of Clinton approval levels that once appeared invincible.

Clinton has struggled to tamp down long-standing worries on the left that she is too close to powerful interests on Wall Street and in Hollywood. But her efforts now are also aimed at more moderate Democrats concerned that her early pace was too placid or regal.

She did little to dispel the image of privilege by spending the night of the Republican debates raising money in Hollywood and posing for a picture with reality television star Kim Kardashian.

Former House speaker and Republican presidential candidate Newt Gingrich said that Clinton is vulnerable and that the Democrats look like “a gerontocracy.”

Clinton is 67; Sanders and Biden are in their 70s.

The debate left him feeling good about the Republicans’ chances next year, Gingrich said.

“I’m pretty optimistic. We have a lot of work to do, but we’re moving in the right direction,” he said.

Although Clinton’s campaign leaders insist they are not running scared, her allies say the new injection of energy is partly an effort to counter negative coverage of her e-mail foibles and her falling poll numbers.

Her campaign says Clinton’s slide in popularity was inevitable as the well-known former secretary of state moved fully into the role of a presidential candidate.

“You’re going to get nicked up a bit” over a long campaign, chief strategist and pollster Joel Benenson told reporters Wednesday. “This is a marathon, not a sprint.”

Clinton’s favorability rating shrank from 44 percent to 37 percent between June and July, according to an NBC-Wall Street Journal poll released last week. Other surveys show similar drops and indicate her lead over Sanders has eroded.

Aides say attention to such numbers obscures the unfavorable ratings for Republicans and the fact that Clinton leads every Republican contender in national head-to-head matchups. A new WMUR-University of New Hampshire poll, however, puts Bush, Walker and Sen. Rand Paul (R-Ky.) one or two points ahead of Clinton in that state — a statistical tie that is bad news for her.

Clinton’s lead over Republicans nationally and over the rest of the Democratic field is a thin reed for a candidate with as long a résumé and as much time in the public eye as Clinton, McLean said.

“The only thing she’s got going for her is that Republicans are even more unfavorable and untrustworthy” in national polls, McLean said.

The launch of a $2 million advertising campaign in Iowa and New Hampshire last week was not an emergency response to a drop in support in those early voting states, Benenson said.

“Oh, no, not at all,” Benenson said during a telephone briefing that was itself an example of the campaign’s new posture. Anticipating a barrage of attacks on Clinton at Thursday’s GOP debate, the campaign had offered Benenson for preemptive spin. “These ads have been in the works,” he said. “There’s a story to be told.”

The gauzy biographical spots strike a very different chord than Clinton’s partisan jibes on the stump and her comebacks on Twitter. Republicans are not mentioned. The ads retrace themes of hard work and middle-class striving that Clinton struck when she entered the race in April and cast her as a champion for working people and families.

The campaign chose to run the ads now because it raised enough money to do so, another senior aide said. Clinton brought in more than $45 million between April and July. The campaign had set a threshold of about $35 million to begin ads, said the aide, who spoke on the condition of anonymity to describe aspects of campaign strategy.

“It’s true she is playing more offense,” said one campaign official, who spoke on the condition of anonymity to discuss internal strategy.

The shift reflects a sense that the time is right to draw attention to what the Clinton team sees as Republican policy positions that are out of step with public opinion, the official said. Clinton has begun regularly criticizing her opponents on same-sex marriage, immigration, and access to abortion and reproductive health care.

“It’s just gearing up. It’s more active and more aggressive,” the official said, as the campaign begins to move past the phase of laying out Clinton’s policy positions one by one.

“This is an important time right now. They are getting a lot of attention, and we don’t see any evidence that the attention is helping them,” the official said of Republicans. “We see evidence the attention is hurting them and their brand. Trump has contributed to that.”

Clinton’s attacks will be limited to Republicans for now, the campaign official and other Clinton allies said.

The first Democratic debate is scheduled for October.

The audience for the tougher language is both Democratic primary voters and general-election voters, according to the campaign, although it is plain that reassuring politically active Democrats that Clinton will scrap with Republicans is a major motivation.

The campaign has been holding outreach meetings with select groups of supporters to discuss the attack strategy against Republicans.

“We want independent voters and general-election voters to mark these moments and have them seep into the public consciousness as much as you can do in August,” when the election is still more than a year away, the campaign official said.

“And we want to have Democratic voters see her doing this, see that she has prosecuted the case against Republicans very effectively.”

Karen Tumulty contributed to this report.