Democratic Party nominee Hillary Clinton downplayed concerns over her health even as talk of contingency plans began to swirl.
Mrs Clinton - who was diagnosed with pneumonia last week and appeared wobbly at a Sept 11 memorial event - told CNN she would be back on the campaign trail within the week. "It's just the kind of thing that if it happens to you and you're a busy, active person, you keep moving forward," she said.
Last night, her team said she will resume campaigning on Friday with an event in Washington, but if she was not feeling well the plan could change, reported MSNBC.
Democratic Party leaders have been out reassuring the public about her health.
White House spokesman Josh Earnest told reporters that President Barack Obama is confident Mrs Clinton would bring the same "endurance" to the job of president as she did to the role of secretary of state.
Her husband, former president Bill Clinton, similarly said Mrs Clinton was "doing fine", stressing that her condition on Sunday was not a symptom of a more serious illness.
He told CBS News: "Well, if it is, it's a mystery to me and all of her doctors... On more than one occasion, over the last many, many years, the same sort of thing happened to her when she got severely dehydrated, and she's worked like a demon, as you know, as secretary of state, as a senator, and in the years since."
The campaign also said it was going to release more medical records this week to head off concerns about the 68-year-old's health. Health has become a larger-than-normal concern in this year's race, given the age of the two candidates. Mrs Clinton will be the second-oldest first-term president if elected, while Mr Trump, 70, would be the oldest.
Both have released only partial medical records, with Mr Trump so far issuing nothing but a hastily written four-paragraph letter.
Assurances from the Clinton camp on Monday came as some had already started to look into what would happen if the nominee could not continue.
Legal experts say the by-laws of the party already lay out what would happen during an unprecedented last-minute withdrawal.
According to the by-laws of the Democratic and Republican parties, a special meeting of the party leadership is convened if the party needed to fill a vacancy on the national ticket. This would be a much narrower group than the thousands that gathered for the conventions.
Where things get a little complicated is after a replacement - say Senator Bernie Sanders or Vice- President Joe Biden - is picked.
Deadlines for registering candidates in the different states have passed and the party would have to go through the courts to change the name currently on the ballots.
Alternatively, they could also rely on the electoral college to vote for the replacement candidate.
The electoral college system means that American voters do not actually directly pick the president. After the popular vote is counted, electors allocated to each state then cast the votes for president according to the election results in their state. State electors from states won by Mrs Clinton would then logically vote for the replacement Democratic Party nominee.
The complications would come in if the Republicans tried to challenge in the courts the validity of either the name change on the ballot or the right of electors to vote for someone not on it. There are few precedents for such a scenario. No candidate of a major party has ever withdrawn from a general election.
And while such a scenario remains highly unlikely, former Democratic National Committee chair Don Fowler was already calling for his party to draft a contingency plan quickly.
"Now is the time for all good political leaders to come to the aid of their party... I think the plan should be developed by six o'clock this afternoon," he told Politico.
