Kamala Harris and rival Donald Trump campaigned in battleground states Sunday seeking 11th-hour advantages in a deadlocked White House race, as new polling shows the vice president underperforming among some traditional Democratic voter demographics.

Harris was in North Carolina, a state hard-hit by a hurricane two weeks ago that devastated several communities and left more than 235 people dead across the US Southeast, as she seeks to counter Trump's claims that federal agencies have done little to help storm victims.

"Moments of crisis, I believe, do have a way of revealing the heroes among us," she said during a speech at a church in Greenville, a North Carolina city where African-American students staged the historic 1960 sit-in at a segregated lunch counter in a fight for civil rights.

Without naming the former president, Harris then called out those who had been "lying about people who are working hard to help folks in need, spreading disinformation."

Trump heavily focused on the key election issue of migration at a rally in Arizona, promising in an often meandering 92-minute speech that he would hire 10,000 new US border guards if reelected. 

The Republican earlier used a Fox News interview to float the idea of using military force against Americans he described as "the enemy from within." 

"We have some sick people, radical left lunatics," he said, without specifying whom he had in mind. "And it should be very easily handled by -- if necessary, by National Guard or, if really necessary, by the military."

Federal law generally bars use of the military for civilian law enforcement, though there are limited exceptions.

Meanwhile, police said a man in possession of a shotgun and a loaded handgun was arrested on Saturday near a Trump rally in California. 

The Secret Service said the former president, who has been targeted in two assassination attempts since July, was not in any danger during the incident.

- 'Left behind' -

Polling shows Harris and Trump neck-and-neck, including in the seven swing states that are likely to determine the outcome of the election.

It also shows Harris has so far failed to stanch the flow of Latinos from the Democratic fold toward Trump, even as he pushes his sharply anti-immigration message.

Data from the latest New York Times/Siena College poll show Harris underperforming other recent Democratic nominees among likely Latino voters, currently earning just 56 percent of the demographic compared to Trump's 37 percent, a margin of 19 points.

While Harris has large advantages with women, particularly women of color, she is struggling to gain traction with Black male voters, a growing number of whom are leaning toward the brash Republican.

As the 59-year-old was campaigning in North Carolina, her boss, President Joe Biden, was in Florida assessing the damage from more recent Hurricane Milton. 

He announced $600 million in aid for areas affected by that storm as well as by Hurricane Helene, which struck with deadly force in late September.

With just 23 days before the November 5 election, Trump and his running mate Senator J.D. Vance continue to thrust the federal disaster response squarely into the presidential race.

Asked on ABC Sunday talk show "This Week" whether Trump has been accurate in describing the federal response as incompetent, Vance said "it's to suggest that Americans are feeling left behind by their government, which they are."

- Eyes on Pennsylvania -

Both candidates hold campaign events in the biggest swing state prize of all, Pennsylvania, on Monday. 

A Harris heavyweight surrogate, Democratic ex-president Bill Clinton, was also on the trail Sunday in battleground Georgia, where he spoke at Mount Zion Baptist Church, a historically Black congregation.

Speaking at a rally in Greenville later on Sunday, Harris accused Trump of "not being transparent with the voters," pointing to his refusal to release his medical records, or sit down for an interview with CBS's 60 Minutes news program. 

"It makes you wonder, why does his staff want him to hide away?" she said. "Are they afraid that people will see that he is too weak and unstable to lead America?"