The stunning revelation that the US supreme court has privately voted to overturn Roe v Wade immediately thrust one of the most polarizing issues in American life to the forefront of the national political debate, and now abortion rights promises to reshape the dynamics of the coming midterm elections.

The draft opinion, written by Justice Samuel Alito and obtained by Politico in a highly unusual and possibly unprecedented leak from the nation’s highest court, would strike down Roe, the landmark supreme court decision that has guaranteed access to abortion for nearly half a century, and a subsequent 1992 decision – Planned Parenthood v Casey – that largely upheld that right.

“Roe was egregiously wrong from the start,” Alito wrote in the draft opinion labeled “first draft”, which was not expected to be finalized for at least several more weeks and could change in its final form. The question of whether abortion should be legal, Alito argues, is best answered by individual states.

In a statement on Tuesday, the supreme court confirmed the authenticity of the draft report but cautioned that it “does not represent a decision by the court or the final position of any member on the issues in the case”.

Nevertheless, as the revelation reverberated across Washington, protesters gathered in front of the supreme court on Tuesday morning, shouting loudly enough to be heard by the members of Congress arriving for work at the Capitol. From the White House, Joe Biden urged voters to elect political leaders who would act to protect abortion access and reproductive rights, irrespective of the supreme court’s final decision.

“If the court does overturn Roe, it will fall on our nation’s elected officials at all levels of government to protect a woman’s right to choose,” Biden said in a statement. “And it will fall on voters to elect pro-choice officials this November. At the federal level, we will need more pro-choice senators and a pro-choice majority in the House to adopt legislation that codifies Roe, which I will work to pass and sign into law.”

Strategists were preparing for a decision that either weakened or reversed Roe, but the leak upended the expected timetable and, potentially, the legislative agenda.

The Senate majority leader, Chuck Schumer, said he would bring legislation to the floor that would codify abortion access in federal law. But the measure is unlikely to garner the 60 votes needed to pass the Senate. A similar measure passed by the Democratic-controlled House last year does not even have the support of all 50 Democratic senators.

“A vote on this legislation is not an abstract exercise. This is as urgent and real as it gets,” Schumer said on the Senate floor on Tuesday. “We will vote to protect a woman’s right to choose and every American is going to see which side every senator stands.”

In anticipation of such a ruling by the supreme court, Republican-led states have proposed, and in many cases already passed, a cascade of restrictive anti-abortion laws. Conservative activists are pushing a nationwide ban on abortion if Republicans recapture control of Congress in November, as they are favored to do.

In a flurry of statements and fundraising emails, Democrats argued that the erosion of reproductive rights was a reason to support them in the November midterms.

“Republicans just gutted Roe v Wade, the Constitution’s guarantee of reproductive freedom, and will ban abortion in all 50 states, if they take over Congress,” the New York congressman Sean Patrick Maloney, the chairman of the Democratic Congressional Campaign Committee, wrote on Twitter. “Only Democrats will protect our freedoms. That is now the central choice in the 2022 election.”

Democratic lawmakers and candidates condemned the expected decision, and vowed to protect access to abortion.

“As a pro-choice pastor, I’ve always believed that a patient’s room is way too small for a woman, her doctor, and the United States government,” wrote the Georgia senator Raphael Warnock, one of the most vulnerable Democrats up for re-election this cycle. “I’ll always fight to protect a woman’s right to choose. And that will never change.”

The Minnesota senator Tina Smith put it more bluntly: “This is bullshit.”

Polls have consistently found that most Americans want Roe to remain the law of the land, and the vast majority want abortion to remain legal in at least some cases.

A decision overturning Roe would be the culmination of a 50-year project by anti-abortion activists to remake the federal courts by using their political clout to pressure Republicans to appoint and confirm reliably conservative majorities.

In 2016, Donald Trump sealed his support among conservative voters by vowing to nominate supreme court justices who opposed abortion. His presidency yielded three conservative justices, all of whom are reportedly in the majority voting to strike down Roe. They also refused to block a novel Texas law that has effectively outlawed abortion in the nation’s second-largest state.

But instead of celebrating the draft ruling, Republican lawmakers on Tuesday were almost singularly focused on the leak, expressing outrage over the disclosure that was likely to further undermine faith in the judiciary as an independent branch of government.

“Last night’s stunning breach was an attack on the independence of the supreme court,” the Senate minority leader, Mitch McConnell, wrote in a statement. “By every indication, this was yet another escalation in the radical left’s ongoing campaign to bully and intimidate federal judges and substitute mob rule for the rule of law.”

Chief Justice John Roberts said in a statement that he had ordered the marshal of the court to open an investigation into the source of the leak. “This was a singular and egregious breach of that trust that is an affront to the court and the community of public servants who work here,” he said.

While the nation awaits a final opinion, pro-choice activists are urging supporters to keep making their voices heard.

“Let’s be clear: this is a draft opinion. It’s outrageous, it’s unprecedented, but it is not final,” Planned Parenthood wrote on Twitter. “Abortion is your right – and it is STILL LEGAL.”