GREENSBORO (North Carolina) • Mrs Hillary Clinton got back on the campaign trail after taking three days off for pneumonia, and the Democratic presidential candidate faced a more challenging political landscape, with Republican rival Donald Trump rising in opinion polls.
Senior Clinton aides said they always expected the race to the Nov 8 election to be close.
But it was clear from a raft of new polls that Mr Trump had halted a summer swoon after taking steps to give a less freewheeling, more polished performance on the stump.
Mrs Clinton, 68, appeared in good health on a visit to her campaign plane's press cabin while flying to Greensboro, North Carolina, for a rally where she sought to refocus her campaign on the plight of the working class - which has turned out to be a potent theme for Mr Trump.
Leaving the stage to the tune of James Brown's I Got You (I Feel Good), Mrs Clinton told reporters she had kept her pneumonia diagnosis last Friday quiet, telling only senior staff, because she thought she would be able to "power through" the illness and keep campaigning.
"From my perspective, I thought I was going to be fine and I thought that there was no reason to make a big fuss about it," she said.
What has hurt Mrs Clinton, Democratic strategist Bob Shrum said, is not the time taken off from the campaign trail but rather her decision to keep her diagnosis secret until forced to disclose it - which reinforced a perception among voters that she has a penchant for secrecy.
On Sunday, Mrs Clinton nearly collapsed while leaving a ceremony marking the Sept 11, 2001 attacks in New York.
Her illness coincided with a mini-surge by Mr Trump, who has drawn even or taken a slight lead in national polls. Polls in battleground states where the race is likely to be decided showed Mr Trump now leading in Iowa, Ohio, Florida and Nevada, and tied in North Carolina.
Following her appearance in North Carolina, Mrs Clinton was scheduled to appear at a Washington dinner. Her campaign chairman, Mr John Podesta, said the candidate and her aides expected the contest to be close.
"We always expected the race to tighten up, we still feel like we're in a strong position with organisational advantage in Florida and Ohio," Mr Podesta said on Thursday.
"They call these states battlegrounds for a reason."
Democratic strategist Bob Shrum said Mrs Clinton remained the favourite to win the White House, with demographic changes favouring her over Mr Trump, who is heavily reliant on white voters.
What has hurt Mrs Clinton, Mr Shrum said, is not the time taken off from the campaign trail but rather her decision to keep her diagnosis secret until forced to disclose it - which reinforced a perception among voters that she has a penchant for secrecy.
"Fairly or unfairly, what this was taken as was more evidence that she was not transparent and that's what hurts her," Mr Shrum said.
"She has been far more transparent than Mr Trump but she hasn't gotten any credit for it."
Democrats have sought to pressure Mr Trump to release his tax returns, but he has said he will not release them until a federal government audit has been completed. Mrs Clinton has released her tax records.
With the candidates' health in the spotlight, Mr Trump, 70, released details of a recent physical examination on Thursday, a day after Mrs Clinton released specifics on her medical condition.
Trump backers on Capitol Hill said they were heartened by the tightening race after a call on Thursday morning with his campaign manager, Ms Kellyanne Conway, who promised a more policy-driven approach from Mr Trump in the race's final stretch.
"The poll numbers are just looking phenomenal as you move away from registered voters to likely voters," Republican US Representative Blake Farenthold of Texas said.