CLEVELAND - Expectations are soaring.

Cory Booker arrives here a day after helping lead a 15-hour Senate filibuster demanding votes on gun laws, and amid chatter about his chances to become Hillary Clinton's running mate. The lunch crowd of roughly 300 Democrats sipping iced tea in a Westin ballroom buzz about the Senate blockade and one of their party's rising stars.

Far from New Jersey, many here are already familiar with Booker, a testament to his political celebrity, talent for grabbing attention and broad personal appeal. Others know his name - but need a closer look.

"I want to learn more about him," says Kathleen Arthur, wearing an orange T-shirt promoting tougher gun laws. "He might become vice president."

Booker's recent two-day swing in key battlegrounds - Ohio and Florida - shows why many Democrats see him as one of their party's most potent young messengers.

But they also represent a test of Booker's trademark optimism. In this year of discord and anxiety, as voters from the Rust Belt to the English Channel vent their anger, Booker is betting big on optimism.

Can it work?

In Cleveland, the answer is resounding.

Booker, 47, is at his energetic best, weaving a liberal policy agenda, humor, and compelling storytelling with a sweeping call to action.

On this day, he excises his go-to platitudes and adds statistics and policy points, illustrated with evocative metaphors.

"It's like your parents leaving you a house, and you've done nothing to keep it up," he says, bemoaning the crumbling U.S. infrastructure. "You let the roof cave in, you let the steps creak and eventually break, and then that's what you want to pass on to your children?"

But Booker's most powerful moments come when he enlists massive, generational themes - equality, cooperation, the common good - and adorns them with enough quotations to fill a high school yearbook.

In 38 minutes he cites King and Kennedy and Lincoln and Langston Hughes and Frederick Douglass and Stokely Carmichael and the Declaration of Independence.

His voice rises as he casts this election as an existential choice - "another American inflection point."

A hotel worker pokes his head out of the kitchen doorway to listen.

"When there is fear and there is frustration, we cannot look at America and say we will descend into hatred - we've got to say, 'we will rise,' " he says, paraphrasing Maya Angelou.

He repeats we will rise over and over as he builds toward a climax about the unity that drove the civil rights movement, D-Day, and the moon landing.

"And now, we have to decide for ourselves, in the face of hate, will we rise up with love?" he asks.

The crowd responds by bolting to its feet as Booker tells them Ohio can make the difference, and his final shouted words are drowned out in applause.

The knock on Booker has long been that he puts on a great show, but is only so-so at governing. That his famous stories - rescuing a woman from a fire, saving a freezing dog, shoveling out snowbound neighbors - fueled hype that outpaced his work as mayor of Newark.

But even his critics concede: Few politicians can stir a crowd like this.

Arthur, the activist still measuring Booker up, is near tears as the speech ends. "I have a fire in my belly," she says.

On stump, on Snapchat

The last six months have marked Booker's return to the limelight.

After arriving in the Senate with a reputation that transcended politics, he kept quiet his first two years, paying his dues the same way outsized names like Clinton and Al Franken did before - though he did show up on the last Colbert Report, singing alongside Alan Alda and George Lucas.

This year, he has pivoted. He released a book, United, took a book tour, and then hit the trail as a key Clinton surrogate.

He campaigned in Iowa, New Hampshire and 12 other states, and stumped for Senate candidates. For a day he ran Clinton's Snapchat account.

She, in turn, said Booker "has more energy and charisma than anybody else I know."

David Pepper, chairman of the Ohio Democratic party, says Booker "represents the next generation of political leadership."

"It's very hard usually for a senator from one state to have a national profile. He's one of the few who does," says Pepper, who has known Booker since the two overlapped at Yale Law School in the 1990s. "He's about as positive a force as there is in politics today."

With his fresh face, cross-cultural reach, and youthful following, Booker checks many key boxes as a running mate for Clinton, who has struggled with young voters and doubts about her authenticity.

But three years into his first Senate term, Booker would face questions about his readiness to be commander-in-chief, and if the ticket won, his ascension could actually hurt Democrats' chances of retaking the Senate: a Republican, Gov. Christie, would choose his replacement.

Booker would also rather avoid a role running mates often play: attack dog.

At his events in Ohio and Florida, he doesn't hit any Republican by name, other than a few jabs at a fellow senator, Marco Rubio. His Ohio speech assails "one leader" who insults women and minorities - but he never says Donald Trump.

Kathleen Hall Jamieson, an expert in political communication, likens Booker's rhetoric to the kind that lifted Barack Obama to the White House as she argues that uplifting messages can still win.

"Both parties need voices that are positive and aspirational in a year when there is too little of that," says Jamieson, director of the University of Pennsylvania's Annenberg Public Policy Center.

But there is also risk: To voters who feel shortchanged by Obama's promise of change, Booker might come across as naive, Jamieson says. "It's easy to say, 'I've heard that before - what did it deliver?' "

A selfie and a smile

For a moment, no one notices Booker.

In Cleveland's airport, he looks like just another guy waiting for his JetBlue flight to Florida, eyes on his phone as he scrolls through the New York Times app for the latest on the gun debate.

The next day, though, he's recognized - and repeatedly stopped for photos - as he arrives at a burger joint by the beachside resort hosting Florida Democrats' annual gala.

Booker, the keynote speaker that night, obliges with a smile, throwing an arm around admirers and taking their phones to snap the pictures himself.

One politico asks for a shot with his daughter. "You'll thank me later," the dad tells her.

Done, Booker slides into a booth and scans a menu thick with beef, bacon, and milkshakes. The faithful vegan orders a vegetable platter with extra hummus, and grabs for the broccoli when it arrives.

He explains his insistence on positivity by describing a walk along the National Mall, with its tributes to King, Lincoln, and Jefferson.

"Are there any monuments built to demagogues? I just don't think so," he says. "We're a nation of hope, of high ideals. I believe we're a nation of love."

Nice sentiment - though hardly reflected in this acrid election year.

"I don't necessarily have that gear" to go negative, Booker says. "At a time when this country wants authenticity, I'm not going to be inauthentic in the way I attack."

He laments that Rubio - similarly young and telegenic - went "into the gutter" against Trump. "I just thought it was off his brand and hurt him."

Yes, Booker talks about "brand."

He says his trips for Clinton, his fund-raising for other Democrats, and his expansive use of Twitter (and Instagram, Facebook, and Snapchat) are not self-serving, but give him an audience to advance his policy goals.

A Democratic president and Senate, he says, "is going to help me do a lot for New Jersey."

He dodges questions about the VP slot: "I'm going to do my best not to answer."

But many believe the senator is building toward bigger plans - including a potential presidential run.

Traveling the country, meeting local officials and donors - "there are a lot of benefits to that," says Matthew Miller, a Democratic strategist.

And even if he's not on the ticket this year, Miller says, Booker belongs on the short list of potential keynote speakers at the Democrats' national convention in Philadelphia.

He would fit the mold of past speakers - Obama in 2008, Julian Castro in 2012 - young, rising, and reflecting a diverse voter base.

A nerd from the burbs

Booker's biography illustrates some of his draw: black senator who grew up in the suburbs, played football at Stanford, went to Oxford and Yale, lives in Newark, has superstar friends, nerd tendencies (check out his Star Trek love), speaks Spanish, and drops a little Yiddish.

Admirers see him through their own prisms. In Ohio, state Rep. Emilia Sykes, 30, hails him as an avatar of young black leadership.

"We don't just have Barack Obama and that's it," Sykes says. "We have plenty more figures who will be able to step up."

Angela Shuckahosee, a Clinton delegate who heads a Cleveland tenants' group, raves about how Booker moved into public housing in Newark. Shuckahosee says she first heard about him through her less politically active twin sister, who forwarded Booker's tweets and "wants to marry him."

In Florida, Tallahassee Mayor Andrew Gillum, 36, says Booker's run inspired his own entry into politics. "So many of us have ambitions and hopes for where he's ultimately going to end up," Gillum says.

And Jayne Chapman, 70, a Democrat from Boca Raton, recalls seeing him shoveling those driveways - and adds that she was glued to C-SPAN during the recent filibuster.

His stand with Sen. Chris Murphy (D., Conn.) demanding votes on gun laws has poignance here in Florida, just days after the Orlando massacre.

"There couldn't be another more meaningful time for him to be here," says Allison Tant, chair of the state's Democratic party. She calls him "a rock star" and says, "There are a lot of people who want him to be the vice president."

Indeed, behind her Booker is surrounded, posing for more photos.

David Moosmann, 21 and working for a local congressional campaign, says that in a time of pessimism, people want something to uplift them.

But first, he gets his selfie, and says, "That was sooooo cool!"

@JonathanTamari