US Vice-President Kamala Harris poked at Republican Donald Trump during a fancy fundraiser on Sunday, telling donors that as she campaigns around the country her "crowds are pretty big" -- before heading to Nevada for a rally at the same venue where the GOP nominee appeared two weeks ago.

During the presidential debate, Harris appeared to get under Trump's skin when she said people were leaving his rallies early because of his rambling speeches. And she's kept it up on the campaign trail.

She also has moved into what Trump considers his terrain -- immigration -- with a Friday visit to the border town of Douglas, Arizona. It was her first trip to the US-Mexico border since taking over for President Joe Biden atop the Democratic presidential ticket.

Harris' four-day West Coast trip has been crafted with dual purposes: She was opening and closing with stops in Sun Belt battlegrounds -- Arizona and Nevada -- where the vice-president is trying to shore up support as Trump pounds her relentlessly over illegal migration. And her mid-stay in California was devoted to hauling in campaign contributions from donors in her blue home state.

Harris' border visit in Arizona seemed to irk Trump. The GOP leader has spent two days railing about the vice-president during his rallies, upping his personal attacks against her, claiming she was responsible for a border "invasion", and stirring up unfounded fears that she'd usher in lawlessness if elected.

Harris gave the same response she usually does to his insults, even despite Trump calling her "mentally impaired".

"We just see the same old tired show from the same old tired playbook," she told a Los Angeles crowd of donors, some who shouted "boring!" in response.

Harris has warned the race is as close as it could possibly be, a "margin-of-error" race. But on Sunday in Los Angeles, she added, "The election is here and let me be clear. We are going to win."

The fundraiser was full of celebrities -- Stevie Wonder, Kegan-Michael Key, Sterling K Brown, Demi Lovato, Jessica Alba and Lili Tomlin. Performing for the crowd -- Halle Bailey and Alanis Morissette.

The vice-president is continuing to notch Republican support. Former Arizona Senator Jeff Flake became the latest to endorse her. He credited Harris with a "fine character and love of country" and said he wants a president who does not treat political adversaries as enemies or try to subvert the will of voters.

Flake, a longtime critic of the former president, joins a list of anti-Trump Republicans who have said they will vote for the Democratic ticket, including Dick Cheney, the deeply conservative former vice-president, and his daughter, Liz.

But Maryland Senate candidate Larry Hogan, a former Republican governor and a sharp critic of Trump, said Harris has yet to earn his vote, though Trump won't get it.

In Nevada, where Harris was holding a rally Sunday night, all voters automatically receive ballots by mail unless they opt out -- a pandemic-era change that was set in state law. That means most ballots could start going out in a matter of weeks.

Harris will be back in Las Vegas on October 10 for a town hall with Hispanic voters. Both she and Trump have campaigned frequently in the city, highlighting the critical role that Nevada's six electoral votes could play in deciding an election expected to be exceedingly close.

Trump held his own Las Vegas rally on September 13 at the Expo World Market Center, where Harris was to speak on Sunday. She's also held events at the same venues that Trump used in Milwaukee, Atlanta and suburban Phoenix.

During a campaign stop in Las Vegas in June, Trump promised to eliminate taxes on tips received by waiters, hotel workers and thousands of other service industry employees. Harris used her own Las Vegas rally in August to make the same promise.

Fully doing away with federal taxes on tips would probably require an act of Congress. Still, Nevada's Culinary Union, which represents 60,000 hospitality workers in Las Vegas and Reno, has endorsed Harris.

Ted Pappageorge, the culinary union's secretary-treasurer, said the difference between the duelling no-taxes-on-tips proposals is that Harris has also pledged to tackle what his union calls "sub-minimum wage", where employers pay service industry workers small salaries and meet minimum wage thresholds by expecting employees to supplement those with tips.

"That shows us she's serious," Pappageorge said.