Andrew Yang got a sign that his top campaign issue is resonating when, he said, Joe Biden sidled up to him during a commercial break at the first presidential debate last month.

“No matter what happens, Andrew, you and I need to sit down and talk about the fourth industrial revolution because I’m terrified that we’re going to gut the middle class,” Yang recalled Biden telling him.

“And I said, ‘Hell yeah, Joe,” Yang said Tuesday during a campaign appearance in San Francisco. “This is a very, very positive thing that the message is getting through in ways big and small.”

As Yang puts it, the U.S. is “in the third inning” of “the greatest economic and technological transformation in the history of the country,” and its leaders have done little to prepare for the changes ahead.

One of his solutions: Offer a universal basic income of $1,000 a month to every citizen, regardless of income. He says it’s not meant to replace existing safety-net programs. He would pay for it with a 10% value added tax, a form of taxation used in 160 countries where goods are taxed at every point along the supply chain.

“We’re going to create a trickle-up economy,” Yang said, adding that even Republicans would support a universal grant because “cash is very hard to demonize.”

While he’s been the idea’s only proponent in the Democratic field, Yang said the relationships he has developed with his fellow candidates make him “very confident that we’re going to mainstream the issues that are important to this campaign in the days and weeks to come.”

He’s started to get enough traction to pull him out of the race’s bottom tier. Even though he’s polling at only 1.6% in the RealClearPolitics.com amalgamation of major polls, that’s more than bigger names like New Jersey Sen. Cory Booker and Minnesota Sen. Amy Klobuchar. In New Hampshire, he’s polling at 2.3%, slightly ahead of former Texas Rep. Beto O’Rourke, according to RealClearPolitics.com.

Unlike some of his better-known rivals, Yang is in good position to make the debate stage Sept. 12 in Houston, when the qualification requirements double. To qualify, candidates must receive 2% support or more in four national or early-voting-state polls and donations from at least 130,000 donors. Yang is one of eight candidates who have met the donor threshold.

There’s a quirkiness to Yang’s campaign that has caught on with a sliver of voters. His acolytes — dubbed “The Yang Gang” — chant “PowerPoint” at his rallies. They wear ball caps that say “MATH” on the front — for “Make America Think Harder” — a nod to the business entrepreneur’s pride in being “numerate data-driven,” as he told The Chronicle’s “It’s All Political” podcast.

“He appeals to me as a moderate — he’s not ideological about everything like the others,” said Sage Kitamorn, a 36-year-old independent voter from San Francisco who got his “MATH” cap signed Tuesday by the candidate.

Yang’s campaign platform is chock full of policy planks not seen elsewhere. He wants to offer free marriage counseling, thinks mixed martial arts fighters should be free to unionize and says the NCAA to compensate student athletes.

Yet in many ways, Yang shows the mark of the rookie politician that he is. He struggled to be heard in the first Democratic debate last month, only speaking for 2 minutes and 50 seconds — roughly a quarter of the airtime that Biden, a politician for five decades, grabbed. On Twitter after the debate, Yang contended that his microphone was turned off unless he was called on. Plus, he said, a debate “requires very specific behaviors that feel very forced” and promised to do better at the next debate later this month in Detroit.

Second, I feel bad for those who tuned in to see and support me that I didn’t get more airtime. Will do better (my mic being off unless called on didn’t help) and glad to have another opportunity in July (and afterwards)! — Andrew Yang (@AndrewYang) June 28, 2019

But in other ways, he’s outperforming some longtime politicians. Yang has raised $4.6 million — more than former Housing and Urban Development Secretary Julián Castro, Colorado Sen. Michael Bennet, former Colorado Gov. John Hickenlooper and Montana Gov. Steve Bullock. It’s far less than Vermont Sen. Bernie Sanders, who has raised $46 million so far, but it is not the lowest in the field.

An earlier version of this story misstated what “MATH” stands for on Yang supporters’ caps. It stands for “Make America Think Harder.”

Joe Garofoli is The San Francisco Chronicle’s senior political writer. Email: jgarofoli@sfchronicle.com Twitter: @joegarofoli