It's now clear that Clinton, despite a raft of political advantages that make her the envy of rivals from both parties, faces a stubborn obstacle in her quest to win the Democratic nomination.
She must weather the summer of Sanders.
In New Hampshire on Saturday, he drew hundreds of supporters -- or curiosity-seekers -- during a weekend campaign tour. As a senator from neighboring Vermont, Sanders is a familiar figure in the first-in-the-nation primary state, which helps explain why he now trails Clinton by only 8 points, according to a new CNN/WMUR New Hampshire Primary poll
"I have been attacked recently: 'Bernie is extreme.' I don't think these things are extreme," Sanders told an audience of about 500 people in Nashua. "This is the agenda of America, what the American people want. Don't let anyone tell you or define me as extremist or out of touch with the American people."
He has emerged as the leading progressive alternative to Clinton, consolidating support from Democrats who had been clamoring for Elizabeth Warren to enter the race.
"This is a different type of campaign -- a people's campaign," Sanders said, railing against the influence from what he calls the "billionaire class."
While the Clinton campaign has been carefully tracking the Sanders momentum for the last month, particularly the Obama-size crowds he's been drawing in Iowa, New Hampshire and beyond, aides say she has no immediate plans to go after Sanders.
Taking an aggressive posture could not only elevate him even more in the eyes of liberals, it could also backfire and create deep divisions inside the Democratic Party that she is still far more likely than not to lead.
Several Democrats close to the campaign, even some who have been underwhelmed by the first three months of her candidacy, tell CNN that Clinton and her team are far from panicking.
Clinton plans response to Sanders
But Clinton does intend to respond to Sanders -- and the progressive wing of her party -- in a far more nuanced way this summer. She intends to take several steps, including:
** Escalating her direct challenge of Republicans, increasingly calling them out by name, in an effort to cement her image as a fighter for Democratic interests. There's nothing more energizing to Democrats than a few well-honed attacks on Jeb Bush, Marco Rubio, Scott Walker and the rest of the Republican field.
** Delivering a series of policy speeches throughout the summer, amplifying her call for social and economic issues that animate progressives. She intends to tackle college affordability, women's pay equity and paid family leave -- among other issues -- in hopes of making her candidacy more acceptable to voters who may be more inclined to favor Warren or Sanders.
** Campaigning aggressively in Iowa and New Hampshire, the first two contests in the primary fight, to demonstrate that she knows she must work hard to capture the Democratic nomination and will put in the work needed to win over any skeptical liberals.
Clinton struggles on empathy question
Since jumping into the race, Clinton has struggled to persuade voters that she is empathetic. The latest New Hampshire poll
shows 45% say Sanders is the candidate who cares the most about people like you, compared with 24% who believe Clinton is.
Sanders, a political independent who proudly calls himself a socialist, had seven stops on his weekend New Hampshire campaign schedule. As he hailed the Supreme Court decision that made same-sex marriage a right in all 50 states, Sanders reminded voters Saturday that he has long been supportive of gay rights.
While he did not reference Clinton directly, he made it clear that he opposed the controversial Defense of Marriage Act that President Bill Clinton signed into law. It was an implicit reminder that Hillary Clinton has come around far more recently to the liberal cause.
"Not too many people voted against it, but I did," Sanders said. "Back in 1996, that was a tough vote."
The New Hampshire poll shows that many Democrats are responding favorably to Clinton's candidacy, including 74% who say they have a positive impression of her. She also is more trusted to handle the economy and health care, two of the leading domestic issues in the contest.
Clinton has been spending considerable time in June raising money, eyeing the first campaign fundraising deadline next week. A series of interviews with local Democratic leaders in New Hampshire and Iowa suggests there is a hunger among party activists for more -- not less -- of Clinton.
Desire for a contest
There is also a hunger for a competitive primary fight.
"There are two kinds of groups," said Jean Pardee, the Democratic chairwoman in Clinton County, Iowa. "There are those who are concerned that Hillary's baggage will keep her from winning. There is another group who likes the blunt, outspoken answers that Bernie Sanders gives."
Pardee and other party leaders say the growing interest in Sanders is only a warning sign for Clinton.
"As of now, I don't see it as a problem," Pardee told CNN. "I think it will make her and her staff work a little more carefully and harder. They certainly won't take anything for granted, as in 2008 they did."