When the former Starbucks CEO Howard Schultz held an event promoting his new book in his home town of Seattle on Thursday evening, his audience was greeted by dozens of protesters holding signs decorated with coffee cups and chanting: “Pick a party.”

The news that Schultz is exploring a potential run for the presidency as an independent candidate sparked a backlash from leading Democrats this week, some of whom believe such a move could help hand the White House to Donald Trump again in 2020.

“We are absolutely petrified that Howard Schultz will come in and take votes from the Democrats and hand us another four years of Donald Trump,” said Chris Petzold, founder of Indivisible Washington’s Eighth District, a local advocacy group which organized the protest across the street from the theatre, where a long line of people headed into the event.

“If he wants to run, let him run as a Democrat,” said Dow Constantine, local government official for King county, Washington. “Come join the progressives and, yes, Howard, the moderates, who have already announced for the presidency from the Democratic party.”

Howard Schultz speaks with moderator Monica Guzman during his book tour in Seattle, Washington, on 31 January. Photograph: Jason Redmond/Reuters

This was the third stop on Schultz’s US book tour to promote From the Ground Up: A Journey to Reimagine the Promise of America. It was also the latest example of the intense pushback he has received since announcing in a CBS interview on Sunday that he was considering a run for the 2020 presidency as a “centrist independent”.

But in the city where Schultz cut his teeth as the CEO of Starbucks and built his caffeine empire, the disapproval felt just a bit more personal.

“If your hometown doesn’t support you, what’s that say?” said Petzold.

Inside the Moore Theatre, however, the mood was a bit more upbeat. At least 1,500 people had come to this free event to hear Schultz speak about his book and political aspirations.

When Schultz walked on to the stage, the audience applauded and cheered loudly. And when he defended his potential independent bid by saying that it would be an opportunity to unite the country “under one banner, the American flag”, the crowd responded just as enthusiastically.

“I will do nothing on any level to proceed if I thought that in proceeding I would in any way persuade Americans to vote and re-elect Donald Trump,” he said. “That is not going to happen.”

Schultz told the audience that he and his staff have devoted the better part of the year poring over data and polling.

“If we get to spring and summer, where we have not yet made a decision and we look at the numbers and they don’t look like there’s a path, then I’m not going to proceed,” he said. “But at this point my mind is open.”

The pushback against his potential presidential bid has centered fairly heavily on this third-party issue. During his book launch in Manhattan on Monday, hecklers interrupted his speech, with one person saying: “Don’t help elect Trump, you egotistical billionaire asshole!”

Others have questioned why he doesn’t run as a Democrat, given that he has supported the party in the past. When the interviewer brought up this point during the Seattle event, the audience erupted in applause.

People protest Howard Schultz’s possible presidential run in Seattle, Washington.

Schultz explained that he thought both a Trump win and a Democratic win could have a negative impact on the country.

“Take me out of the equation. If Donald Trump is re-elected, we’re going to have four more years of just a disaster level of leadership in the country and our standing in the world,” he said. “If a Democrat should win, I have no confidence … that we’re going to see any change whatsoever in the toxicity of what Washington DC currently represents.”

Schultz worked at Starbucks for about 36 years, serving much of that time as CEO, before leaving the position last summer. During his tenure, the company experienced incredible expansion, growing from only a handful of stores to almost 30,000 around the world.

But the business itself was notably born in Seattle. The “original Starbucks” (technically it’s the original Starbucks’ second location) is still located in the heart of the city. Adorned with the business’s original mermaid logo, the shop draws a steady stream of tourists, while its notoriously long line tends to keep locals away.

At this point, it’s kind of, we’ve all got to band together and vote for the person who is the least orange Alyssa Brandt

When Schultz announced he was considering a presidential bid, it seemed appropriate to go back to where it all began.

On Wednesday afternoon, the shop was a bit quieter than usual. Some customers said they supported Schultz’s bid, while others said they felt very strongly that he shouldn’t move forward with it.

Alyssa Brandt, 24, who grew up in Seattle but now lives in Hawaii, had a more moderate perspective.

“At this point, it’s kind of, we’ve all got to band together and vote for the person who is the least orange,” she said. “And if everyone could band together and vote for him, awesome.”

There was also a handful of people who, as they sipped their Starbucks drinks, didn’t actually know the name Howard Schultz at all.

Blake Gerald, 27, who was visiting from Mississippi, confessed he probably only recognized Schultz’s name because of all the news lately about his potential run for the Oval Office. He questioned whether Schultz has the name recognition to actually make a dent in what is surely going to be a stiff competition.

“I just don’t think another rich person running for office is going to inspire a whole lot of excitement,” he said. “Maybe with a hell of an ad campaign. But even then, getting his name out there, amongst all the others that are more well known and actually have experience in politics.”

On Thursday, Schultz seemed ready and eager to face the challenge.

“I know how stiff this climb will be and I know it hasn’t been done before,” he said. “But that doesn’t mean that it can’t be done. It would be un-American to say it can’t be done.”