When a butterfly flutters in Springvale South can a sitting Prime Minister be ejected from the Lodge? That’s the question Labor MPs are pondering this morning after Bill Shorten’s 11th-hour press conference switching his personal support away from Julia Gillard and towards Kevin Rudd.

Right up until last night Shorten was holding on to his default position — playing dead on the leadership, even as the state party moved around him, to avoid going down in history as the “faceless man” that knifed two prime ministers.

But the pointy-end proclamation was in fact the end point of months of wailing within Victorian Labor that can be traced to Lyndhurst MP Tim Holding’s mysterious decision to quit politics in February, triggering a byelection in the apparently ultra-safe seat deep within Labor’s multicultural heartland. Martin Pakula — the National Union of Workers-aligned upper house MP with strong leadership credentials — quickly threw his hat in the ring for the gig.

In Victoria, long considered Gillard’s “rock”, the thinking within Shorten’s Australian Workers Union circle was always that Labor could safely hold onto the crown jewels even if the rest of the country was aflame with anti-Gillard agitation.

When the Lyndhurst returns started trickling in on April 27, party powerbrokers were horrified. With the Liberals failing to field a candidate, Pakula was forced to preferences against Family First with just 40.1% of the primary vote, a massive 15 points less than Holding had achieved at the 2010 state election. Lyndhurst takes in Springvale (east of Springvale Road) and Dandenong South. The Southvale booth, within Simon Crean’s federal electorate of Hotham, suffered the largest individual booth swing of 23.9% — from 59.6% of the primary vote to 35.7%. Springvale South copped a 22.7% swing. Crean, on a margin of 14%, was ropeable. The rest of the seat takes in Mark Dreyfus’ Isaacs (margin: 10.4%) and a sliver of Anthony Byrne’s Holt (14%).

“Lyndhurst just put us in a foetal position,” one Labor MP told Crikey this morning. “Basically, the shelling started from then on.”

“It showed that the great myth that Victoria was safe had exploded. Shorten’s strategy of keeping his powder dry and letting the other states burn was over.”

Then, five weeks later, a second sentinel event occurred. On June 4, JWS Research polling was published by News Limited. Almost surreally, it showed Isaacs was now in play with a 15.4% swing. Alarm bells, and Shorten’s mobile, started ringing off the hook. It’s understood Shorten then took the extreme step of commissioning private polling in his seat of Maribyrnong, that he holds by 17.5% on the new boundaries.

“That polling just f-cking freaked people out,” the MP said. “The shelling from that polling just went white hot.

“It showed that the great myth that Victoria was safe had exploded. Shorten’s strategy of keeping his powder dry and letting the other states burn was over.”

MPs strolling around their electorates were constantly badgered with references by members of the CALD community to Rudd — if he were leader they would have shifted their vote. Key Victorian AWU powerbrokers began pushing upwards. South-East MP Luke Donellan and former AWU state secretary Cesar Melhem (by then in the upper house in Pakula’s vacated spot) were crucial.

“There were basically phone calls from the AWU to Bill to say you’ve got to move,” the anonymous MP said. “It was getting intolerable.”

Barrie Cassidy’s pronouncement on Insiders on June 9 that Rudd would take over before the election belled the cat. Cassidy is considered very close to Shorten and sometimes takes meals with him.

Elsewhere, things were also gradually falling into place. Most of the NSW Right had moved en masse in March, with the only state holdouts Tony Burke, Chris Hayes and Sharon Bird. And right-aligned general secretary Sam Dastyari was on hand in Canberra this week, partly for a meeting with the national secretariat but also to ensure the vote proceeded smoothly. The South Australian Left, led by Mark Butler, were well on the way, and Tasmania was also sufficiently wobbly.

As Shorten strolled up to the press pack at 6.30pm last night, the numbers had already moved beyond the 51 required for a tie. Barring a miracle, the Rudd camp was home free.