The short version of how Americans lost their right to terminate a pregnancy might be summed up in one name: Trump.

The real estate tycoon and reality-TV star first shocked the world by winning the US presidency, then rewarded his base by confirming three supreme court justices to a nine-member bench, thus rebalancing the court to lean conservative for a generation to come.

That short road led to Dobbs v Jackson Women’s Health Organization, an opinion released this week in which supreme court justices voted to overturn the landmark case Roe v Wade, which in 1973 granted a constitutional right to abortion.

The end of federal protection for abortion is expected to lead to 26 states banning the procedure immediately or as soon as practicable, affecting tens of millions of US women and people who can become pregnant.

The decision comes even though about 85% of Americans favor legal abortion in at least some circumstances. Why, and how, a decision opposed by a majority of Americans came about has everything to do with political power, experts said.

The anti-abortion movement is “the best organized faction in American politics”, said Frederick Clarkson, an expert on the Christian right and a senior research analyst at Political Research Associate, a progressive thinktank in Massachusetts.

“They understand they’re a minority of the population, of the electorate, and certainly a minority set of views on reproductive rights issues,” he said. “But because they know that, they’ve found effective ways of maximizing their political clout by being better organized than numerically greater factions who are less well organized.”

Put another way, he said, the anti-abortion movement “mastered the tools of democracy to achieve undemocratic outcomes”.

The currents that led to the Dobbs decision are among the most powerful in American politics today. Over decades, a religious movement prevailed by harnessing the forces of polarization, the erosion of constitutional norms and the manipulation of US democracy, scholars said.

“It’s not like we’ve had this slow erosion of abortion rights,” said Neil Siegel, an expert in constitutional law and professor at Duke University who clerked for former liberal Justice Ruth Bader Ginsburg. Instead, justices issued an opinion that “is utterly dismissive of what has been constitutional law for literally five decades”, and was “repeatedly affirmed by justices appointed by both parties”.

The conservative-leaning court will shatter one more constitutional norm, issuing a once-in-a-lifetime reversal, after another event without modern precedent: the leak of a supreme court draft opinion. Even before Dobbs was released, the leak spelled out the doom of Roe v Wade.

“The court is not the institution I served,” said Siegel.

Today, abortion is among the most partisan issues in the US, with Republicans and the anti-abortion movement so closely aligned there is little daylight between them. In the 1970s, however, abortion was seen as a “Catholic issue”, with both pro-choice Republicans and anti-abortion Democrats in Congress. The supreme court voted in favor of Roe v Wade by a 7-2 margin.

Some of this transformation reflects “deliberate changes by the anti-abortion movement, some of it is structural changes to US democracy, and some of it is just luck,” said Mary Ziegler, visiting professor at Harvard and a professor of constitutional law at the University of California Davis.

Contrary to popular belief, there was no immediate political backlash to Roe v Wade. In the years that followed, important bills banned the federal government from paying for abortions, but a constitutional amendment to outright ban the procedure failed.

It wasn’t until the late 1970s that Republican strategists, such as Paul Weyrich, saw abortion as an issue that might unlock the votes of millions of white evangelical Christians, alongside opposition to women’s rights and to desegregation court rulings. The plan worked: Catholics and white evangelical Protestants were brought into uneasy alliance with Republicans.

“Back in the 70s and 80s, when the anti-abortion movement was maturing, I remember events where you would see one Catholic bishop sitting on stage uncomfortably with evangelicals,” said Clarkson.

It would be decades before evangelical Christians and Catholics entirely fused their modern agenda, with abortion, gay marriage and religious freedom as top issues. Nevertheless, the new alliance soon produced a “moral majority” that buoyed Ronald Reagan’s campaign. Like Trump, Reagan initially supported “liberalized” abortion law, before he later promised to oppose abortion as president.

This political realignment was helped along by the Voting Rights Act of 1965, which constitutional scholars argued forced segregationist southern Democrats into real competition with Republicans for the first time.

“You don’t understand reproductive politics in this country if you don’t understand racial politics in this country,” said Loretta Ross, founder of the SisterSong Women of Color Reproductive Health Collective, a reproductive rights organizer in Georgia.

“I believe the current restrictions on abortion, birth control and sex education are all designed to compel white women to have more babies,” said Ross. “I’m not convinced they want more brown or Black babies,” even though brown and Black women would be disproportionately affected by abortion bans, she said.

This political realignment also brought Republicans distinct structural advantages based on the architecture of the US constitution – a force Siegel describes as “rural favoritism”.

The two-chamber Congress is made up of the House of Representatives, whose seats are based on population, and the Senate, which grants each state two votes no matter the population. “The constitution has always disproportionately favored rural voters, but it didn’t always favor one party,” said Siegel.

As Republican senators began to represent more white, Christian and rural voters, however, they also gained advantage of a feature baked into the US constitution. Today, Republicans collectively represent 41.5 million fewer Americans than Democrats, even though the Senate is evenly split. As a result, the new conservative-leaning court was confirmed by a body which represents a minority of voters.

“That is reflective of minority rule,” said Siegel.

Republican strategists’ appeal to socially conservative voters also began to substantially redefine what it meant to be Republican.

“The party professionals and establishment Republicans thought they could control them,” said Clarkson. “They were wrong: they became the party.”

The new anti-abortion arrivals pushed for more power, working “to exercise more influence over the composition of the GOP to ensure the nominees would be ideologically pure enough”, Clarkson said.

Demography added urgency to the anti-abortion cause, Siegel said. The Republican party is overwhelmingly white and Christian, but the size of its base is threatened by rapidly changing US demographics as America grows more racially diverse and less religious. White Americans are predicted to be a minority by 2045.

That has pushed Republicans to practice “existential politics”, made each election cycle feel more critical than the last and forced the parties further apart, said Siegel. At the same time, partisan redistricting, known as gerrymandering, has allowed more extreme candidates to win uncompetitive districts, exacerbating polarization.

In the case of Dobbs, power and luck collided when the base elected Trump, a man who once professed to be pro-choice, won the election even as he lost the popular vote and was then offered the rare opportunity to confirm three new justices to the court.

The forces behind Dobbs also show how especially American values – autonomy, liberty and self-determination – will be redefined in a new supreme court era.

“There’s mutual animosity between members of the two parties, but there is more of an asymmetry in terms of how far to the right the Republican party has moved, and willingness to break norms for short-term partisan advantage,” said Siegel. “Or, in the case of the supreme court, for long-term partisan advantage.”

• This article was amended on 24 June 2022 to clarify Frederick Clarkson’s biography.