Ah, a thread on this issue that shouldn't get bogged down in the details of the rights and wrongs of the constitutional crisis, or with the idea it was somehow the last important event in Australian history (hello to a certain kind of national populist conservative, or plain loyalist, both here and overseas). Thank you.
The 1974 double dissolution happening before the middle of the year meant that half the senators had terms set to expire on 30 June 1976; it was widely believed Whitlam would probably hold a House of Reps elections at the same time as the needed half-senate election, even though the Reps' term didn't expire until 1977.
Labor was probably going to lose. The 1974 recession was too nasty, too much a shock for people who'd experienced a generation of the golden age of demand management capitalism after WWII; Whitlam and co were held guilty of throwing it all away. It doesn't matter that the governments and administrations of the UK, US and Canada were in similar boats. Or, at least, it's reasonable to use these contrasts to see federal Labor suffering an election loss somewhere between what Ford experienced in 1976, and what Callaghan probably would have suffered at an early election in 1978, before the British winter of discontent. (The outcomes in the Canadian electoral system are least applicable here.)
The landslide defeat of December 1975 probably can't happen at an election scheduled to Whitlam's satisfaction in '76 or '77.
13/12/75 was Labor at it's weakest vis-a-vis the budgetary situation (which was set to improve with the Hayden budget's forecasts; those mostly came true by the end of the ongoing financial year IIRC), the economy beginning to rebound, the closeness in time to the ministerial scandals of the loans crisis, and simply looking like a dishevelled Old Labor mess thanks to having been unceremoniously thrown out of office when the country was on the brink of a federal public service shutdown in November.
it seems that the Governor General dismissing a sitting prime minister heavily bolstered republican sentiment Down Under
It absolutely consolidated republican sentiment in the ALP. Otherwise, there is no way that Labor MPs and officials from minor states would all have been anti-monarchist by the time of the 1999 republican process. Not just obscure figures, too. It's perfectly reasonable that someone like Peter Beattie, then Opposition leader in the Qld parliament, or Graham Edwards, marginal seat MHR from Perth, could have been monarchists,
if they'd had the choice. But 1975 set the entire party down the road to rock solid republicanism. (Think of it as being like the British Conservative Party's Brexit-at-all-costs stance going into last year's election, immediately after the humiliating intervention of the High Court into the prorogation, not to mention the subsequent split off of soft- and anti-Brexiteers.
Non-negotiable.)
to the point where now both major parties are supportive of becoming a republic.
This is highly contentious. The Coalition has had a lot of republican-inclined people since at least the '90s. But during that time it's also grown a powerful ideologically conservative activism, mythos even, that views the '99 refendum victory, a victory lead by Tony Abbott under the watchful eye of John Howard, as being an end of history/silent majority victory deal. And the defeat of the quixotic recent moderate Coalition prime ministerial experiment, brought down by an ideological/commentariat push that look to Trump and Brexit for inspiration, that now reinforces the old-ish religion. (Need I point out ex-PM Turnbull lead the failed republican movement 20 years ago?) A resurgent, majority monarchism hasn't formally been tested in the Libs and Nats, not recently, but it's totally there. No way it isn't there.
Would no Whitlam dismissal make the Monarchy more popular (or at least make republicans more ambivalent about having a Monarchy?
An eventual constitutional 'crash' is probably coming with the ascent of Charles to the throne. IIRC polling has long reflected less public approval for him than for his mother. The recent drama over his second son and daughter-in-law must reflect on looming weaknesses in respect for the Australian crown, for when we have an aging divorced King succeeding such a well defined, stable monarch as Elizabeth the II has been .
Just because No Dismissal means no 'premature' republican process, it doesn't necessarily signify much else the further we get into the 21st century.
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Fwiw, repeating something I've written here years ago, the biggest substantive result for our system of government in the short- to medium- term with No Dismissal isn't even anything of what I just wrote. It's this: IMO you can't just get to Prime Minister Bob Hawke and Treasurer Paul Keating taking office in 1983, if Labor hasn't first been traumatised by OTL 1975.
It can still happen, but it's much less certain. There's a chain of events that needs the Dismissal to occur first, if you want to get cleanly to the eventual era-of-neoliberalism that emerged under the stable leadership of eighties federal Labor govt.