> [...] but despite the best efforts by the conservative [...]

Those efforts were actually pretty half-hearted. They talked a big game, but they don't actually want to abolish it. (Reminds me of how the UK doesn't really want to face up to a no-deal Brexit, despite lots of brave talk. Or how no government in the UK has so far re-nationalised the railroads, despite re-nationalisation perennially polling high with the general public.)

This is a really good point. Conservatives had two full years to repeal the Affordable Care Act. They had campaigned as a party for "Repeal and Replace" for nearly 10 years, but then they didn't repeal it.

In Australia's case, the same-sex marriage law was approved by 61% of voters in a national plebiscite, a non-binding referendum (officially it was called a "postal survey") before Parliament enacted it.

Legally, Parliament could repeal it tomorrow and ban same-sex marriage again. Politically, that would be impossible without another plebiscite, and there is no reason to believe a new plebiscite would deliver a different outcome; it would almost certainly return the same result, and likely by a bigger margin.

No conservative politician in Australia wants to talk about this. I'm sure some of them are still personally opposed to same-sex marriage, but they all realise trying to repeal it is hopeless, and so they'd rather talk about things that they have some hope of achieving.

Simply put: two of the five justices who voted in favor of Obergefell (the case that legalized same-sex marriage) are no longer on the Court. They have been replaced with justices who would be more likely to vote the other way.

The realignment of the Court, plus this Court's willingness to overturn settled law, together signal that a new law prohibiting same-sex marriage might be allowed to stand if brought before today's Court, returning the US to a country where same-sex marriage is not universally legal.

So I would regard our current regime around same-sex marriage, civil rights, etc. to be subject to not being directly challenged at the Supreme Court.

The Australian Constitution is heavyweight on the mechanics of federal government, and how heads of power are divided between the state and federal governments, and the role of the court to adjudicate, but quite lightweight on peoples "inalienable rights". There's no "bill of rights" - though there are certain principals like "natural justice" and "customary law". Parliaments are empowered to legislate, and that's what they do. So it's comparatively rare that the court will discover some basis to neuter legislation - though it does happen.