If Hillary did drop out, she would be the first candidate in history to do so

A successor for Hillary Clinton must be found immediately in case pneumonia forces her out of the race, a former Democratic National Committee chair has said.

'Now is the time for all good political leaders to come to the aid of their party,' Don Fowler, who chaired the DNC from 1995 to 1997, said Monday. 'I think the plan should be developed by 6 o'clock this afternoon.'

Fowler - who has supported Hillary Clinton since her 2008 presidential bid - said the Democrats risk infighting without a proper contingency plan, Politico reported.

Hillary Clinton's doctor confirmed on Sunday night the presidential candidate has pneumonia. Now a former chair of the DNC says the Democrats must prepare a contingency plan

Plans: Don Fowler, who was DNC chair from 1995-1997, says the Democrats must work now to figure out how to elect a replacement for Clinton in case she drops out of the race

Clinton's doctor confirmed on Sunday night the presidential candidate has pneumonia.

She made the shocking announcement after video surfaced of the 68-year-old collapsing after abruptly leaving the 9/11 memorial service in New York.

The result has left some members of the party - including Fowler - very nervous.

Fowler said that he believes Clinton will get better, but that the risk of party-infighting just two months before the presidential election should be taken seriously.

'It's something you would be a fool not to prepare for,' he said.

The Democratic Party's rules allow for the DNC to name a replacement, but don't provide many guidelines on how the process is to be performed.

And strong support for Joe Biden and Bernie Sanders could lead to fractious arguments if a path forward is not clearly outlined.

'I think you’re likely to have at least discussions and perhaps controversy,' added Fowler.

Loyal: Fowler (center, at a DNC fundraiser) was the chair during Bill Clinton's tenure as President, and has supported Hillary since 2008. But he says a plan is essential

Instead, he argues, Barack Obama and other high-ranking Democrats should figure out now how a replacement for Clinton would be selected, and who that would be.

'There should be a concerted, unified effort on behalf of the president and the Democratic leaders in the House and the Senate and from the officials of the DNC as well - I think unanimity would be absolutely critical,' he said.

'The quicker that unanimity develops, the easier and better the process.'

Clinton has put her campaign on hold and is resting in her Chappaqua, New York, home. Her husband will take over her campaigning duties for the time being.

But if her condition deteriorates significantly, the Democratic Party may be forced to consider their options.

In 1972, Sargent Shriver was selected to replace Thomas Eagleton as George McGovern’s vice presidential nominee, after Eagleton's depression was deemed a threat to the public, should he take over as President.

That's the only time such a switch has been made in Democratic or Republican history.

Should Clinton have to drop out of the race for the White House, here's what will happen:

Democratic National Committee bylaws would come into play

The DNC's guidelines state that, if Clinton was to drop out, it would have to be completely her choice.

Clinton is seen resting her hand on a child's shoulder after leaving daughter Chelsea's apartment on Sunday

If she confirmed she was stepping aside, senior party officials would hold an emergency meeting.

A vote would then be organized among members, with the new name on the ticket having to be elected by a simple majority.

But it is not clear when or how that would take place.

It is likely the Democrats would do improvise slightly in order to choose another candidate.

There would be no special preference given to any candidates who have already been involved in the process.

The Democratic National Committee Bylaws read: 'The foregoing notwithstanding, a special meeting to fill a vacancy on the National ticket shall be held on the call of the Chairperson, who shall set the date for such meeting.'

Then there would be a vote among members to fill the position on the national ticket. The winner would require a simple majority.

However, all of the members who vote would have to be present when they handed over their ballot slips

If one of the Republican candidates died, their party would reconvene the convention.

Could Congress push Election Day back?

Congress sets the date for the General Election. This year it is on November 8, or the Tuesday after the first Monday in November.

They can vote to change the date to extend the time the Democrats have to decide on a candidate - or for Hillary to recover- but it's extremely unlikely.

Voting laws - such as changing elections to weekends - have stalled in Congress frequently. States would also have to pass any regulations and would have to extend their voting regulations.

There is also a strong Republican presence in Congress, and they may not want to pass a measure that gives the Democrats a chance of winning.

Tim Kaine for President?

As the United States Senator from Virginia already has a large donor base, there is a strong chance he would move up the ticket.

He may then pick up running mate himself and carry on campaigning.

However, members of the party would have to cast their vote to get him into that position.

Kaine has no special consideration even though he is on the ticket. If someone else is voted in, Kaine could still be the running mate

As running mate Tim Kaine already has a large donor base, there is a strong chance he would move up the ticket. However he has no special consideration over potential rivals

What about Joe Biden or Bernie Sanders?

Bernie Sanders was Clinton's most viable and strongest opponent during the campaign, while Joe Biden has always been a favorite of the Democratic hopefuls.

Arguably, as two of the more recognized Democrats, they could drum up more support during the general election.

However, they would still have to be picked by members.

Biden has previously stated he didn't want to run. Bernie lost out to Clinton in the primary process, but still has a large support base among members.

Biden has previously stated he didn't want to run, but is still one of the most popular figures in the Democratic Party (he is pictured greeting Philadelphia Eagles wide receiver Jordan Matthews before their game against the Cleveland Browns on Sunday)

Bernie Sanders lost out to Clinton in the primary process, but still has a large support base among members

Could it be Chelsea?

There is a tradition of spouses taking the place of their candidate, but that has typically been when they have died.

For example, Jean Carnahan stood in for her husband Mel after he died in a plane crash three weeks before the Missouri Senate election in 2001. She won, and served for two years in his place.

Future Senator Olympia Snowe first entered politics after the death of her husband, a Maine state representative, in a car wreck.

Former U.S. Representative for California Mary Bono’s long political career began when her husband Sonny died in a skiing incident.

She was first elected to Congress just weeks after her husband died.

But Hillary's husband Bill is prevented from running because of The 22nd Amendment - stating no President can be elected to more than two terms.

Therefore, Chelsea could take her place. There is a concern that she has never held elected office and hasn't made it clear she wants a career in politics.

There is a tradition of spouses taking the place of their candidate. But the 22nd Amendment means her husband Bill (left) cannot run. Chelsea (right) could be the next family member in line to take Hillary's place

Who has faced similar questions before?

Many high-profile candidates have been put under the same scrutiny, but they haven't dropped out.

Rumors about Franklin D Roosevelt’s health dogged his final presidential campaign in 1944.

He carried on regardless, as his aides kept his heart disease a secret. It would kill him in 1945, just a year into his fourth term, prompting Vice President Harry Truman to be sworn in as president.

Republicans Ronald Reagan, Bob Dole and Senator John McCain have all faced questions about their health as Republican presidential nominees.

McCain allowed reporters to see 1,173 pages of medical records after concerns were raised about a cancer scare.

He failed in his bid to become president, losing to Barack Obama in 2008.

Rumors about Franklin D Roosevelt’s health dogged his final presidential campaign in 1944 (pictured). He carried on, as his aides kept his heart disease a secret. It would kill him in 1945, just a year into his third term

Does it depend how quickly she recovers from pneumonia?

Pneumonia is commonly treated quickly and effectively with antibiotics.

Doctors suggest it takes around a week to get over the worst of the symptoms.

If she was considering stepping aside from the campaign, she would have to choose at least a month before.

This would allow the DNC to go through with the voting process.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University, said patients with a mild pneumonia can recover with antibiotics, a few days of rest and good hydration.

That's especially true of someone who does strenuous work, such as a rigorous campaign schedule.

But Clinton does need to take it seriously, some experts said.

People over age 65 have a harder time returning to normal than do younger patients.

Many people her age need a week or more to recover from even a mild case of pneumonia, said Dr Sharon Bergquist, an Emory University assistant professor of medicine who specializes in internal medicine.

'The body needs rest. The more she pushes, the harder it is for her to recover,' she said.