Donald Trump has alluded to Hillary Clinton's health, saying she lacks "physical stamina" for the job.
Hillary Clinton launched the home stretch of her US presidential bid on Monday aiming to solidify her advantages over rival Donald Trump, with both candidates converging on working-class Ohio as ground zero of their 2016 campaign battle.
The Democratic nominee maintains an edge over Republican flagbearer Trump in national polls, has dramatically deeper ground operations in swing states, and trounced Trump in August fundraising.
But Trump's unconventional White House bid, including his campaign's apparent imperviousness to criticism about his harsh rhetoric, assures a tight contest for the next 64 days until the election.
"I'm not taking anybody, anywhere for granted," Clinton told a crowd of more than 1,000 at a Labor Day parade and picnic in Cleveland.
Clinton, after a few days of campaign trail rest, coughed her way through portions of her speech as she suffered one of her worst coughing bouts of the race.
She paused to sip water before managing to quip, in a crackling voice, that "every time I think about Trump I get allergic."
The imagery is sure to fuel critics' theories that Clinton, 68, has serious health problems.
Trump has alluded to Clinton's health, saying she lacks the "physical stamina" for the job.
Clinton debuted her new campaign plane -- with the slogan "Stronger Together" emblazoned on the side -- that will carry her through to the November 8 election, and it hosted guests with whom she has been reluctant to travel until now: reporters.
Under extensive criticism from her rival and journalists for not holding a full press conference in nine months, Clinton welcomed reporters on her plane and briefly entertained questions before taking off from New York.
"I am so happy to have all of you with me. I've been just waiting for this moment," said Clinton, perhaps in gentle jest, to media in the back of her plane.
The Labor Day holiday traditionally kicks off the fast-paced fall campaign season, and Clinton and Trump both beat a path to Ohio to woo voters in the must-win state.
Clinton said she was prepared for the two months of intense political battle ahead.
"I'm ready. I'm more than ready," she said, as she attempts to become the first female US commander in chief.
Republican MessengerHighlighting the intensity of the fight for battleground states like Ohio, Trump and his vice presidential running mate Mike Pence were already on the ground in Cleveland for their own campaign events when Clinton arrived.
As her jet landed, it parked on the tarmac near Trump's with the space of about two football fields separating them.
Like Clinton, Trump has largely avoided having the press corps on his plane, but on Monday he invited some journalists aboard.
Just a week after traveling to Mexico and then returning across the US border to deliver a hardline immigration speech, he assailed Clinton for having "no plan" on immigration.
"What her real plan is, she has total amnesty" and a pathway to citizenship, he said, reiterating his opposition to such a legalization process without undocumented immigrants leaving the country first.
Under Clinton, "people can pour across the border and it doesn't matter who the people are."
Clinton shot back by recalling Trump's meeting with Mexico's President Enrique Pena Nieto and how Trump "can't even go to a foreign country without" triggering a feud with a world leader.
Trump visited a Cleveland diner to meet with union members. He is seeking to capitalize on simmering frustration among blue collar workers over wage stagnation and mediocre job prospects.
"Voters who traditionally haven't voted Republican or haven't voted in a very long time seem to be coming out to support this messenger and this message," Trump's campaign director Kellyanne Conway said.
Trump, 70, trails in polling but dominated the week's political messaging and imagery that included his visit to an African-American church in Detroit.
And while Sunday's CBS News Battleground Tracker shows Clinton, 68, leading Trump in two key states -- by eight points in Pennsylvania and four points in North Carolina -- recent polls show the race tightening nationally.
"The polls are close so Crooked Hillary is getting out of bed and will campaign tomorrow," Trump taunted late Sunday on Twitter.
On The RoadThe first of three presidential debates that are expected to be the most watched moments of the election is just three weeks away.
After hinting last month that he might not participate in all of them, Trump told reporters he was on board.
"I expect to do all three," Trump said on his plane.
Clinton and Trump were each joined by their running mates in Ohio, a signal of the importance each campaign places on the Buckeye State.
Senate Democrat Sherrod Brown of Ohio said there was "more pressure on Trump" than Clinton.
"If Trump loses Ohio he loses the race," Brown told AFP.
"Hillary can lose Ohio and still win because she's going to win Virginia, North Carolina, Colorado," and other swing states, Brown added.