VIRGINIA BEACH, Va. (AP) -- With Labor Day behind them, Donald Trump and Hillary Clinton are pushing ahead in top presidential battlegrounds in the South.
Trump, the Republican nominee, is set to campaign in Virginia and North Carolina on Tuesday, two critical states in his path to the presidency. Clinton, the Democrat, is campaigning in Florida in search of an advantage in the nation's largest swing state. A Clinton victory in Florida would make it virtually impossible for Trump to overcome her advantage in the race for 270 electoral votes.
The day before in swing state Ohio, Trump softened his stance on immigration while Clinton blasted Russia for suspected tampering in the U.S. electoral process.
In a rare news conference aboard her new campaign plane, Clinton said she is concerned about "credible reports about Russian government interference in our elections."
"We are going to have to take those threats and attacks seriously," Clinton told reporters traveling with her from Ohio to Illinois.
Clinton's comments follow reports that the Russian government may have been involved in the hacking of Democratic National Committee emails just days before the party's national convention. The emails, later revealed by WikiLeaks, showed some DNC officials favoring Clinton over her primary opponent, Bernie Sanders — who has since endorsed Clinton for president.
She said Russian President Vladimir Putin appears "quite satisfied with himself" and said Trump "has generally parroted what is a Putin-Kremlin line."
Meanwhile, Trump extended a rare invitation to journalists to accompany him on his private plane from Cleveland to Youngstown, Ohio. The billionaire businessman appeared to shy away from his hard-line vow to block "amnesty" for immigrants in the country illegally.
Any immigrants who want full citizenship must return to their countries of origin and get in line, he told reporters — but he would not rule out a pathway to legal status for the millions living in the U.S. illegally, as he did in a long-awaited policy speech last week.
"We're going to make that decision into the future," Trump said.
Clinton powered through a coughing fit at a Labor Day festival at a Cleveland park, sharply criticizing Trump's recent trip to Mexico as "an embarrassing international incident." Unwilling to allow Trump to modify his immigration stances, she said his address later that night in Arizona amounted to a "doubling down on his absurd plan to send a deportation force to round up 16 million people."
"He can try to fool voters into thinking somehow he's not as harsh and inhumane as he seems, but it's too late," Clinton said.
The former secretary of state flatly said "No," when asked in an ABC News interview whether she'd be willing to accept the Mexican president's invitation to visit the country, as Trump did last week.
"I'm going to continue to focus on what we're doing to create jobs here at home," Clinton said.
Earlier in the day, Trump attacked Clinton's energy level, noting she hasn't followed his aggressive traveling schedule and questioning whether she had the stamina to help bring jobs back to America.
"She doesn't have the energy to bring 'em back. You need energy, man," Trump told reporters.
He added, "She didn't have the energy to go to Louisiana. And she didn't have the energy to go to Mexico."
Clinton's 25-minute question-and-answer session was her first extensive availability with reporters since early December. Beyond Russia, she answered questions about the ongoing controversy surrounding her use of a private email server while secretary of state, which Trump has used to cast doubt over her ability to protect classified information.
"I take classification seriously," she said.
While Labor Day has traditionally been the kickoff to the fall campaign, both Clinton and Trump have been locked in an intense back-and-forth throughout the summer.
The start of full-fledged campaigning opens a pivotal month, culminating in the first presidential debate Sept. 26 at Hofstra University in Hempstead, New York. Polls show Trump trailing Clinton in a series of must-win battleground states, meaning the debates could be his best chance at reorienting the race.
Trump told reporters he does plan to take part in all three presidential debates, joking that only a "hurricane" or "natural disaster" would prevent him from attending.