The numbers game Opening the door: Kevin Rudd at Federal Parliament on Wednesday. Kevin Rudd's supporters were last night considering a high-stakes tilt at the Labor leadership, with supporters on both sides seeking to lock in crucial votes before the final sitting day of Parliament. Senior ministers, including Trade Minister Craig Emerson and others, embarked on a charm offensive on Wednesday to shore up support for Ms Gillard among worried Labor MPs. Entering what is potentially the most vulnerable day of her 2½ year leadership, Ms Gillard has been assured by backers inside the government and by key union supporters in the broader labour movement, that her caucus majority will remain sound and will not crumble in the face of a challenge. Backers maintain she is not for turning. "Julia Gillard is as tough as they make them," Treasurer Wayne Swan said. She's going to beat Tony Abbott because she's focused on the big reforms for the future. For his part, Kevin Rudd has repeated his pledge not to make an attempt on the leadership, leaving only the option of a move by others, or by Ms Gillard herself. In a development transparently calculated to increase the temperature of the burgeoning leadership crisis, the government's Chief Whip and key Rudd numbers man, Joel Fitzgibbon, used a Fairfax Media online interview on Wednesday to publicly stake out the battleground for the looming showdown. He said it would make no sense to change leaders after the May 14 budget. "I think this idea that the party could change leaders between budget day and the September election is just a silly concept," he said. While Mr Fitzgibbon was careful not to openly endorse a change of leaders now, his comments were seen as a deliberate message to undecideds in the caucus that it is now or never. Fairfax Media was told the Rudd camp was also considering a plan to send a delegation of senior figures to the Prime Minister's office calling on her to declare the leadership vacant, with a second option being a petition of signatures from caucus members for a spill. Caucus rules allow for a leadership ballot in circumstances where a minimum third of the caucus put their names to a petition. However, this option is seen as least likely because it requires MPs to show their hand even before the leadership ballot is secured. With MPs hostile to Ms Gillard and convinced the party is headed for annihilation under her leadership itching for the showdown, the tactic of choice to date has been one of maximum pressure, creating a more-or-less permanent sense of chaos in the hope of forcing Ms Gillard to move to clear the air. However, Ms Gillard's backers say that will not be happening and they insist the embattled Prime Minister will lead them to the poll. As the smouldering leadership tensions burst into the open, ministers and influential backbench MPs loyal to Ms Gillard began calling colleagues to shore up her base, with phones running hot. As the penultimate sitting day wore on, it is understood Rudd backers were also trying to crack Ms Gillard's support base, particularly in the Victorian Right faction where the influence of Bill Shorten and Stephen Conroy has ensured a block of votes remain locked in behind the Prime Minister. The Parliament breaks on Thursday for six weeks before the May budget. Mr Fitzgibbon's comments suggest the chances of a leadership change turn on what happens in the final day before the recess - traditionally the most dangerous time for wounded leaders.