The US Supreme Court on Tuesday confirmed that a draft ruling indicating the court may overturn the landmark 1973 Roe vs Wade decision that legalised abortion nationwide was authentic, as Democrats scrambled to respond to the bombshell news and President Joe Biden vowed to try to protect abortion rights.

The court in a news release said that it will launch an investigation of how the draft was leaked to the news outlet Politico. It added that the document — authored by conservative Justice Samuel Alito —does not represent “the final position of any member” of the high court.

“I have directed the Marshal of the Court to launch an investigation into the source of the leak,” chief justice John Roberts said, calling it an “egregious breach” of trust.

Democrats at the state and federal level and abortion rights activists looked for some way to head off the sweeping social change long sought by Republicans and religious conservatives.

Biden said voters will need to elect more members of Congress who support abortion rights so that they can pass legislation making Roe vs Wade the law of the land. The Roe decision recognised that the right to personal privacy under the US Constitution protects a woman’s ability to terminate her pregnancy.

“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,” Biden said.

Democratic-backed legislation to protect abortion access nationally died in Congress this year as the razor-thin majority held by Biden’s party was insufficient to overcome Senate rules requiring a super-majority to move forward on most legislation. Democrats tend to support abortion rights. Republicans tend to oppose them.

California governor Gavin Newsom, after Politico reported the draft decision late on Monday, said that the most populous US state will propose an amendment to its constitution to “enshrine the right to choose,” meaning obtaining an abortion.

“We can’t trust SCOTUS to protect the right to abortion, so we’ll do it ourselves,” Newsom wrote on Twitter, referring to the Supreme Court.

“Do something, Democrats,” abortion rights protesters chanted as they rallied outside the court in the pre-dawn hours against the decision, which would be a triumph for Republicans who spent decades building the court’s current 6-3 conservative majority.

“If the report is accurate, the Supreme Court is poised to inflict the greatest restriction of rights in the past fifty years, not just on women but on all Americans,” Congress’s top two Democrats — House of Representatives Speaker Nancy Pelosi and Senate majority leader Chuck Schumer — said in a joint statement.

Senate Republican leader Mitch McConnell condemned the leak as a “lawless action” that should be “investigated and punished as fully as possible”. McConnell said the justice department must pursue criminal charges if applicable.

In the absence of federal action, states have passed a raft of abortion-related laws. Republican-led states have moved swiftly, with new restrictions passed this year in six states. Three Democratic-led states this year have passed measures intended to protect abortion rights.

Abortion is one of the most divisive issues in US politics and has been for nearly a half century. A 2021 Pew Research Center poll found that 59 per cent of US adults believed it should be legal in all or most cases, while 39 per cent thought it should be illegal in most or all cases.

The abortion ruling, due by the end of June, would be the court’s biggest since former President Donald Trump succeeded in naming three conservative justices to the court — Neil Gorsuch, Brett Kavanaugh and Amy Coney Barrett. The anti-abortion group the Susan B. Anthony List welcomed the news.

“If Roe is indeed overturned, our job will be to build consensus for the strongest protections possible for unborn children and women in every legislature,” said its president, Marjorie Dannenfelser.

“Roe was egregiously wrong from the start,” conservative justice Samuel Alito wrote in the draft opinion, which is dated February 10, according to Politico, which posted a copy online.

The case involves a Republican-backed Mississippi ban on abortion starting at 15 weeks of pregnancy, a law blocked by lower courts.

Based on Alito’s opinion, the court would find that the Roe vs Wade decision that allowed abortions performed before a foetus would be viable outside the womb — between 24 and 28 weeks of pregnancy — was wrongly decided because the Constitution makes no specific mention of abortion rights.

“Abortion presents a profound moral question. The Constitution does not prohibit the citizens of each state from regulating or prohibiting abortion,” Alito said, according to the leaked document.

The news broke with elections looming in November that will determine if Democrats hold their slim majorities in the US Congress for the next two years of Biden’s term.

The Politico report said a court majority was inclined to uphold Mississippi’s abortion ban and that there could be five votes to overturn Roe.

Four of the other Republican-appointed justices, Clarence Thomas and Trump’s 3 appointees, voted with Alito in the conference held among the justices.