HOUSTON — Britt Daniel, the lead singer of the venerable indie band Spoon, has started noticing something unusual on the streets of New York City, where he's been spending time with his girlfriend, thousands of miles away from his native Texas: stickers and T-shirts for Beto O'Rourke.

"Maybe there are some Texans up here," Daniel said in an interview. "But it does seem like even non-Texans have taken a lot of interest in this race. Maybe they just see him as someone who has a future for the party, a future in politics, or maybe they're just genuinely inspired by him."

"It is a phenomenon," added Daniel, who has performed at several events for O'Rourke, who is challenging Republican Sen. Ted Cruz.

Betomania is sweeping the nation — or at least its more liberal enclaves — leading fans to ascribe over-sized ambitions to the underdog Texas congressman, even though polls and prognosticators suggest he may be just weeks away from losing to a man who has made plenty of enemies in both parties.

"BETO FOR PRESIDENT," the comedian Billy Eichner ‏tweeted to his more than 2 million followers, and he's hardly alone.

O'Rourke, a former punk rocker with a message like Obama's and a face like a Kennedy, has seen his star rise so steeply that, for now, he seems to have reached escape velocity from mere politics. For a moment, at least, he's become a cultural phenomenon on the lips and in the hearts of Democrats around the country in a way few outside of Obama and Bernie Sanders have recently achieved before him.

"It's like when the Beatles came to America," Bill Maher said when O'Rourke stepped onto the set of Maher's HBO talk show to thunderous applause.

But if O'Rouke loses, and especially if the margin ends up wider than expected, his star could come hurtling back toward earth, potentially crushing fans' hope for a 2020 bid and exposing him to criticism for spending so much money in a race that was always a long shot.

Jim Messina, who ran Obama's re-election campaign, said O'Rourke has a rare combination of "inspiration, aspiration and authenticity" that moves people as he skateboards his way across Texas.

Rep. Beto O'Rourke carries his daughter Molly during a fundraiser baseball game in Austin. Drew Anthony Smith / Getty Images file

"People are motivated by him as a political leader and a human being," Messina said in an email. "He is authentic, and luckily, authentically cool. For him to play air drums to the Who or skateboard is both authentic and cool. People want to hang out with him."

O’Rourke yard signs have been spotted in Rhode Island, Connecticut and Virginia, and he just announced that he raised more money ($38 million) than any Senate candidate in history for a single quarter.

Danny Deraney, a Hollywood publicist who has worked with celebrities like Justin Timberlake and Madonna, said he hasn't seen Los Angeles this excited about a national politician in years.

"Barack Obama kind of swept everybody off their feet, and I think Beto has done that here, too," he said. "Here in a city that is pretty left-leaning, they see someone who is hopeful for this party, that is not the same old, same old. I think people see him as someone who is refreshing."

Beto O'Rourke on HBO's "Real Time with Bill Maher." Janet Van Ham / HBO

Celebrities and sports stars from LeBron James to Ellen DeGeneres to Tony Dungy to Stephen King have expressed their Beto-love. Steve Kerr, the coach of the NBA champion Golden State Warriors, wants him to run for president. And New York City donors were willing to shell out at least $250 each for a recent O'Rourke fundraiser — even though the candidate only appeared via Skype.

A viral video of O'Rourke defending NFL players' right to kneel during the national anthem garnered more than 67 million views, according to Nico Pitney, the political director of NowThis, which produced it. "(It) was one of our most successful videos this year and the most successful midterms-related video," he said.

O’Rourke, who is giving up his El Paso-area House seat to run, has pledged he will serve his entire six-year term if elected, but so did Obama when he was in the Senate. And when CNN included O'Rourke in a 2020 poll this week, they found him tied with Sen. Cory Booker, D-N.J., and former New York City Mayor Michael Bloomberg.

"Authenticity is intoxicating, and now more than ever," said Jesse Lehrich, a veteran of Hillary Clinton's 2016 presidential campaign.

Besides, how many other candidates could get Willie Nelson to write a song for them and then get to perform it live, playing guitar with the country legend for 50,000 people? Who else inspires Richard Linklater, the famed Austin-based filmmaker, to make commercials for a super PAC supporting their campaign?

And what other politician has ever produced an entire music festival with hipster bands like Spoon and the Polyphonic Spree, where some attendees don't bother sticking around after the candidate speaks, even though the headliner has yet to perform? "Spoon might have sold out many shows across the country, but for one night, Beto O'Rourke was the rock star the crowd came to see," The Dallas Observer wrote.

None of this is remotely common for a Senate campaign.

To find a comparison, some analysts have reached all the way back to Robert F. Kennedy, who drew huge crowds when he ran for Senate in New York in 1964 and then quickly turned around to run for president before being assassinated.

Rep. Joe Kennedy III, D-Mass., stumped for O'Rourke in McAllen on Saturday and recalled appearing in the same venue with his uncle, Sen. Ted Kennedy, during a swing for Obama in 2008. "This hall was not as full as it is this morning,” Kennedy said, according to The Dallas Morning News.

O’Rourke's weekday rallies attract hundreds. In Houston, he packed a gym at Lone Star College in the morning, spoke to at least 1,000 in Cypress in the afternoon, then addressed many more at a large outdoor concert-rally with rappers Bun B and and Willie D.

Ariana Gordon, a high school senior, told NBC News it was "mind blowing" for her to finally get to see O’Rourke in person after watching videos of him online. Other young people said they might not vote this year were it not for O'Rourke.

Meanwhile, O’Rourke has become something of a heartthrob for the "resistance" set.

"Why does he look so perfect doing even the most simple things?" the women's magazine Elle gushed about a video of O’Rourke petting a chubby bunny. "Beto's like your energetic, young math teacher who got you very hot and bothered about fractions."

The third-term congressman has also managed to avoid taking collateral damage from the Democratic civil war that erupted out of the Sanders-Clinton presidential primary.

O'Rourke aligns with the progressive wing of the party on most policy issues and has the full endorsement of Sanders-allied groups, but he's also a member of moderate New Democrat Caucus in Congress.

"We are big Beto fans," said Matt Bennett of the centrist Democratic think tank Third Way. "He's not with us on every single thing, but his main campaign themes have been very close to what we think a national narrative should be. And the happy warrior approach is just right for running against a horrible person like Cruz or Trump."

O’Rourke was born and raised in El Paso, a border town where he acquired his Hispanic nickname, even though he is of Irish descent. Boyish looking at 46, he has three kids whom he often name-checks in public, along with his wife, Amy, who worked with him at a technology company until they sold it last year. Elected in 2012, he and his past — which includes a DUI arrest — went largely unnoticed until he decided to run for Senate last year.

Since Beto spent the summer in the Texas heat on a road trip to all 254 counties, Ellen Degeneres surprised him with a personalized wearable fan to help keep him cool. Michael Rozman / Warner Bros.

Unsurprisingly, all the attention has provoked a bit of backlash.

Some Democrats have complained publicly that the $38 million O'Rourke raised last quarter could be better spent in more competitive races that happened to feature less dynamic candidates, though he has resisted calls to share the bounty.

Media critic Jack Shafer, meanwhile, has called for a moratorium on new O'Rourke profiles, writing in Politico that he hasn't seen anything like Betomania "since the press corps fell in love with Barack Obama."

And Cruz has insisted O’Rourke is merely using the Senate race as a stepping stone (even though the Republican senator himself ran for president before his first term was over). "He's pursuing the national Democratic activists in Iowa, New Hampshire — not El Paso," Cruz told reporters last week.

"Beto is the new RFK. He's a natural. You can't train that, you can't focus group it, it either is or it isn't. He's more of a natural than Barack Obama was," said Claude Taylor, a Democratic strategist who founded the Mad Dog PAC.

"But he has to win in Texas," Taylor added. "If he wins in Texas, he'll be the Democratic nominee in 2020."

And if not?

"If he doesn't win in Texas and doesn't become president," Taylor continued, "he'll become No. 2 on the greatest Democratic presidents we never had, after RFK."