While Hillary Clinton’s doctor has assured the American public the Democratic presidential candidate is “recovering nicely” from pneumonia, it appears her party is preparing for every eventuality.

Mrs Clinton has already cancelled a California fundraising trip after falling ill at a 9/11 ceremony, renewing speculation about her health barely eight weeks from election day.

Mrs Clinton was taken to her daughter Chelsea’s New York apartment to recuperate after the stumble.

“Secretary Clinton will not be travelling to California tomorrow or Tuesday,” spokesman Nick Merrill said, hours after the 68-year-old abruptly left the Ground Zero memorial in New York.

Mrs Clinton’s doctor said she has been suffering from pneumonia and “became overheated and dehydrated”.

“Secretary Clinton has been experiencing a cough related to allergies,” Doctor Lisa Bardack said in a statement. “On Friday, during a follow-up evaluation of her prolonged cough, she was diagnosed with pneumonia.

“She was put on antibiotics, and advised to rest and modify her schedule,” Dr Bardack said. “While at this morning’s event, she became overheated and dehydrated. I have just examined her and she is now rehydrated and recovering nicely.”

The health scare has raised concerns as to why she had failed to disclose the health information and what implications it may have for the remainder of the US election race.

Possible replacement candidate

Mrs Clinton can only be replaced as the nominee if she decides to step down, which she appears unlikely to do.

Nonetheless, respected US political journalist David Shuster has quoted a Democratic operative as saying the party has entered “unchartered political territory”.

Mr Shuster’s unidentified source said the Democrats may hold an emergency meeting to consider a possible replacement, but selecting a new nominee would only arise if Mrs Clinton decided to withdraw.

Clarification from dem operatives @HillaryClinton pneumonia: Expect emergency DNC meeting to CONSIDER replacement. #HillarysHealth

— David Shuster (@DavidShuster) September 11, 2016

Top dem: "we can make contingencies, argue, plead with @HillaryClinton, but DNC bylaws are clear her nominee status now totally up to her."

— David Shuster (@DavidShuster) September 12, 2016

Were Mrs Clinton to step down, primaries rivals Joe Biden and Bernie Sanders would be likely to linked to filling the vacancy.

According to Democratic Party rules, the national committee is responsible for filling the position. Party officials each cast one vote at a special meeting and the winner is whoever gains the majority.

Not the first health scare

Mrs Clinton suffered a coughing fit while campaigning in Cleveland last week, which was dismissed by her campaign as allergies.

Mainstream media never covered Hillary’s massive “hacking”
or coughing attack, yet it is #1 trending. What’s up?

— Donald J. Trump (@realDonaldTrump) September 6, 2016

Mrs Clinton has previously been in the news for her health issues.

In December 2012, she developed a blood clot after sustaining a concussion and while a 2015 letter from her doctor described her as being in “excellent health” and “fit to serve” in the White House, it noted that her current medical conditions included hyperthyroidism and seasonal pollen allergies.

Ronald Reagan was the United States’ oldest president after assuming office at the age of 69.

If elected, Republican candidate Donald Trump would be older than Mr Reagan was on election day, while Ms Clinton would be just a few months younger.

The medical scare comes as the latest Associated Press election poll points to a tightening nationally in her race against Mr Trump.

“But Hillary Clinton still has the edge in the states she’ll need to win in November,” AP said.