I’m torn between Citizen’s United and the one that rolled back Roe v. Wade.

Citizens United.

Without Citizens United, there would be no Dobbs.

Bush v Gore

I would like a constitutional scholar to answer this question. I'm not qualified to answer.

Dredd Scott.
Had the court ruled him a human being and not property, then the entire slave trade would have been nullified. Roberts reminds me of Taney in many ways.

I'd read a novel detailing how that alternate timeline plays out.

or even Buckley V Vallejo and there'd be no CU

The best answer is almost surely going to be something the average person has never heard of but had some sort of fundamental effect 150 years ago.

I would be very surprised by that. Like the other poster said, it’s almost certainly Citizen’s United. Without it there wouldn’t be any of the erosion of regulation that we’ve seen blast through the US in less than two decades.

Citizens United

Marbury vs Madison

That’s an odd one. Please explain further why you think that.

Santa Clara County v. Southern Pacific Railroad

For those not familiar, it's the ruling that established that the equal protection clause in the 14th Amendment applies to corporations, so that they are persons under the law. Fun fact: Technically, the court didn't even decide that, the Reporter of Decisions (who was a former railroad company president) wrote that in the headnote and the Court rolled with it.

ETA: This precedent is how corporations could even have 1st Amendment rights in Citizens United.

Runner up: Village of Euclid v. Ambler Realty Co.

This decision allowed zoning laws as a valid exercise of police power, and has let the United States FUBAR most of its landscape.

Revlon, Inc. v. MacAndrews & Forbes Holdings, Inc.

(Although this is Delaware Supreme court, it's still the national precedent)

"Despite the expanse of precedent that Revlon has engendered in the more than 20 years since its issuance, the Revlon doctrine remains alive, well and surprisingly vague in terms of its scope and its application."

Basically it's about fudiciary responsibility, and has been used by shareholders to bludgeon board/CEOs to maximize profits over all other considerations... the engine behind enshitification

https://en.wikipedia.org/wiki/Dodge_v._Ford_Motor_Co.

Not U.S. Supreme, but important in that it led to shareholder value being a primary value for companies.

But somebody else already mentioned another case that set up CU to succeed. Without that CU wouldn't be an issue.

There may have been more steps before too.

But really, initially, there were very early US cases that actually properly treated corps as property, not people. Even forcefully revoking their business charters when they were found to no longer be serving the community but harming it.

I don't understand how it could be law that corps had to be incorporated as legal entities, with the people's permission via the gov of the people, that for centuries their right to exist was utterly temporary and revokable, and that they were legally only treated as owned tools, but then recently courts decided they had personhood and human rights?

Seems like earlier precedent disagrees.

The civil war kicks off with a Confederate sympathizer instead of Lincoln as President. American alt history doesn't even take the typical "Two Americas" fictional path, it just goes straight up slave empire and joins the Scramble for Africa from the foothold in Liberia.

Dobbs v. Jackson Women's Health Organization

https://en.wikipedia.org/wiki/Dobbs_v._Jackson_Women's_Health_Organization

Wickard v Filburn

Dredd Scott was overruled by the 13th and 14th amendments to the constitution.

Fun fact: one of the reasons the court decided that Blacks weren't fully human was that, if they were, they would have to be granted the right to keep and bear arms. The court couldn't countenance such a thing.

100% citizens united. its the reason roe v. wade was rolled back.