The Democratic nominee's effort to win over voters who twice put Barack Obama in the White House -- and who represent her best chance of victory in November -- will reach new intensity this week in the run-up to her first crucial debate clash in seven days.
Young, college-educated and minority voters formed the backbone of Obama's majority in 2008, helping to put once reliably Republican states like Virginia and North Carolina in the Democratic column and shore up the battered incumbent in swing states like Ohio and Florida in 2012.
But recent polls indicate the race tightened dramatically in recent weeks, with GOP nominee Donald Trump on a roll. They suggest that Clinton is lagging behind Obama with younger voters and that she has failed to kindle the enthusiasm that drove them to the polls four and eight years ago.
Questions are also mounting about the scale of likely turnout among black and Hispanic voters, who are expected to vote disproportionately for Clinton but could let her down if they do not show up in sufficient numbers in battleground states. Obama delivered a direct appeal to these voters over the weekend at the Congressional Black Caucus dinner where he made a passionate plea to his supporters to show up in November for Clinton.
After appealing to forums of African-American and Hispanic leaders in recent days, Clinton will travel to crucial Pennsylvania on Monday to highlight the stakes for millennials.
She previewed the likely thrust of her remarks last week in North Carolina in a more personal, emotive stump speech that she retooled while laid up with pneumonia.
"I am running for young people like so many of you here who dream of changing our world for the better," Clinton said.
In that speech, the Democratic nominee also reached out to other sectors of the Obama coalition, including LGBT voters, African Americans and those who secured health care under the current president.
Clinton's running mate, Virginia Sen. Tim Kaine, made a forceful push for millennial votes on NBC's "Meet the Press" Sunday, arguing that on the issues young people care about most, like climate change, women's health, college affordability, immigration reform and LGBT equality, there was only one possible choice in November.
"It's on our shoulders to make the case. But on at least five litmus test issues, the differences between Hillary Clinton and Donald Trump are vast," Kaine said.
Clinton's need to improve her standing among young voters has become apparent in recent polling. A Quinnipiac University poll this month found that Clinton was backed by 31% of voters aged 18-34 while 29% favored Trump. But 44% of that group said they would vote for Libertarian Gary Johnson or Green Party leader Jill Stein.
Other polls have also shown Clinton needing to improve her standing among the younger demographic. If she does not, it could harm her election chances because she is far more dependent on the youth vote than Trump, as the core Republican vote skews much older.
A CNN/ORC poll last week had Clinton leading Trump by 54% to 29% among voters under the age of 45. But she's running behind Obama, who beat Romney 60% to 37% among the same group in 2012.
While the former secretary of state has work to do to electrify the Democratic coalition, she could not have better allies. Most prominently, Obama himself, enjoying some of the best approval ratings of his presidency, is emerging as a passionate, adamant fighter for her cause. First lady Michelle Obama is also taking on a key role. Following her acclaimed speech at the Democratic National Convention this July, she told young voters in Virginia last week that their choice in November would decide whether they could afford a college education and keep their health care when they graduate.
Even Clinton's bitter primary rival, Bernie Sanders, who became a rock star on college campuses and among young voters, is beginning to become more prominent as an advocate warning of the dangers of a Trump presidency.
However, transferring support from one candidate to another is not just a simple matter of passing the baton.
Obama's popularity among Democrats seems intimately attached to the President himself. His efforts to boost Democrats in mid-term elections in 2010 and 2014 had little effect, and his record on picking winners in off-year races is also patchy. It's left the impression that his is a uniquely "Obama" coalition that cannot be easily bequeathed to a successor.
That may be one reason why Obama's appeal to black voters at the Congressional Black Caucus dinner on Saturday was so striking; he figuratively put himself on the ticket in November, urging African Americans to vote for him and his legacy.
"My name may not be on the ballot, but our progress is on the ballot," he said.
"After we have achieved historic turnout in 2008 and 2012, especially in the African-American community, I will consider it a personal insult, an insult to my legacy, if this community lets down its guard and fails to activate itself in this election," Obama said in strikingly direct remarks. "You want to give me a good sendoff? Go vote."
Obama's press secretary Josh Earnest told CNN's "New Day" on Monday that the President's comments were aimed at voters who were turned off by the negativity of the campaign that the "stakes are too high" to tune out.
"I think the impact is to send a clear message to the President's supporters across the country that even though his name isn't on the ballot, he feels passionately about the outcome of this race," Earnest said.
The process of transferring Obama's African-American support to Clinton was given a significant lift by Trump's clumsy effort to lay to rest the "birther" controversy over his repeated false claims that the President may not have been born in the United States, and hence wasn't eligible for the country's highest office.
Though the GOP nominee finally admitted on Friday that Obama was indeed born on American soil, he gave the controversy fresh life by claiming inaccurately that Clinton's 2008 campaign started the furor and that he ended it -- despite pushing the rumor years after Obama produced his birth certificate.
"If you would ask me to come up with one thing that would ruin Donald Trump's momentum over the last three weeks, I would say bringing up the birther thing," said Kevin Madden, a former top Romney strategist, on CNN's "State of the Union Sunday. "In many ways it has brought up new questions and in many ways it has put the spotlight again on Donald Trump in a very negative way."
For her part, Clinton, despite facing the historically daunting task of trying to win a third consecutive White House term for her party, is hugging Obama close.
She paid a fulsome tribute to the President at the CBC dinner and vowed to work tirelessly for a strong African-American turnout in November.
"I want you to know I'm not taking your vote or anyone's vote for granted," she said. "I need your help over the next 52 days to bring our campaign across the finish line together."
Trump's cause, however, has been boosted by a string of recent polls showing that the GOP nominee has all but neutralized Clinton's big convention bounce. And his campaign is suggesting that she will fail to pull off the kind of high turnout among key Democratic constituencies she needs to win in November.
"Bernie Sanders had an event yesterday in Ohio for Hillary Clinton. There were 150 people there," Trump campaign manager KellyAnne Conway said on CBS "Face the Nation" Sunday. "That's like a second wedding where I come from. This is not a big movement for Hillary Clinton."
While the activity of last week and the coming one suggests that the Clinton campaign is concerned about its candidate's progress in reassembling the Obama coalition, the countdown to Election Day could serve to concentrate the minds of Democratic voters.
Young voters are notoriously less likely to show up at the polls than older ones, but they confounded conventional wisdom when they repeatedly answered Obama's call in primary elections and general elections.
In 2012, Republicans backing Romney were adamant that Obama would never recreate the kind of historic turnout, especially among black voters, that he had managed in 2008 when he leveraged the historic potential of the first African-American presidency.
It was only on Election Day, when returns started trickling in from key counties in swing states from Florida to Ohio, that the Romney brain trust learned how wrong they were.
But with Clinton's fate on the line, that coalition is now facing its final -- and most daunting -- test.