The 43rd Parliament of Australia could be entering uncharted waters.
Constitutional crisis or not?
Constitutional expert Prof. George Williams explains the three scenarios that could emerge from a Labor leadership change.
The question looming large over Canberra is whether a change of the Prime Ministership to Kevin Rudd - still by no means a given - would spark a constitutional crisis unlike anything seen before, even the dismissal of Gough Whitlam.
Assuming there is a change back to Mr Rudd, some of the many possible outcomes include Tony Abbott as Prime Minister and an early election with Mr Rudd as PM until then.
The most extreme scenario includes the Governor-General, Quentin Bryce, being forced to fly out of the country to protect the integrity of her office and NSW Governor Marie Bashir being drafted in to do her job.
With the assistance of Anne Twomey, constitutional law professor at Sydney University, here are some of the scenarios:
1. Rudd takes the leadership and survives a no confidence motion on the floor of Parliament.
He would need the support of five of the seven crossbenchers. Tony Windsor has indicated Mr Rudd would not get his vote, while Rob Oakeshott and Peter Slipper have said they would decide if the situation arose. Kevin Rudd can count on the support of Bob Katter, Craig Thomson and Adam Bandt. In this scenario, Mr Rudd would be able to determine the date of the election and would not necessarily have to run to the polls.
2. Rudd takes the Labor leadership but loses a no-confidence motion.
A "constructive vote" would mean a vote of confidence in Mr Abbott would follow a vote of no-confidence in Mr Rudd. In this scenario, the Governor-General would almost certainly have to appoint Mr Abbott as caretaker Prime Minister until an election can be held.
3. Bill Shorten emerges as a "circuit breaker" leader
As the mother-in-law of Mr Shorten, the Governor-General would be cornered by a perceived conflict of interest. Ms Twomey said: "The Governor-General would have the trust of the people but the perception of a conflict of interest would be too great. She would probably have to leave the country and appoint Marie Bashir as the governor of the largest state [NSW] to do her job.
4.Julia Gillard remains Prime Minister and a September 14 election.
Julia Gillard survives the spill and the September 14 election proceeds.