John Roberts, the U.S. chief justice, has announced an investigation into a leak showing that the supreme court provisionally voted to overturn the landmark 1973 Roe v Wade case that legalized abortion nationwide.

Publication of the draft opinion by the Politico website on May 2 night sparked demonstrations outside America’s highest court, condemnation from Joe Biden and fears that the judiciary has suffered profound damage to its reputation for independence.

In a statement on May 3, Roberts confirmed the authenticity of the document written in February and said: “To the extent this betrayal of the confidences of the court was intended to undermine the integrity of our operations, it will not succeed.”

He added: “I have directed the marshal of the court to launch an investigation into the source of the leak.”

Washington was sent into a whirl of speculation over who was responsible for the biggest leak in the modern history of the court – the judicial equivalent of “Deep Throat,” the FBI source that disclosed secrets about the Watergate scandal – and whether they should be considered a leaker or a whistleblower.

Some said it was probably a law clerk for one of the court’s liberal justices who wants to put Justice Samuel Alito’s majority opinion in the public domain in the hope that, witnessing the fierce backlash, one of the conservatives on the court might change his or her vote.

Others guessed it might be a source on the conservative side wanting the justices to be on record so they will feel locked in and unwilling to change in case they been seen as caving in. A third possible motive was floating the decision early to take the sting out of the final, incendiary announcement expected next month.

Edward Fallone, an associate professor at Marquette University Law School in Milwaukee said: “It’s unprecedented. Even those few instances where a law clerk, after leaving the court, wrote a ‘tell-all’ book was viewed as unprecedented then, but for a draft opinion in the midst of the process to come out, I can’t think of any single example.”

The source remains a mystery, but Fallone suggested a law clerk is most likely. “They tend to be younger and more passionate. I would assume other staff with access to draft opinions are a little more professional and discreet. But we just don’t know yet.”

The investigation announced by Roberts seems likely to scrutinise law clerks for the liberal justices: Stephen Breyer, who retires later this year, Sonia Sotomayor and Elena Kagan.

Fallone added: “The suspicion would be that by demonstrating extreme public reaction, they’re trying to perhaps cause one of the conservative majority to have second thoughts.

“It’s also possible that it’s one of the law clerks for a conservative justice, that there might be someone who’s wavering – I guess it might be [Brett] Kavanaugh – at the very broad nature of Alito’s opinion. It might be the thought of a conservative law clerk that it will force Kavanaugh to stay in the majority and not look like he’s backtracking.”

Kavanaugh told his Senate confirmation hearing that Roe v Wade was “settled as a precedent of the supreme court.”

The leak is a particular blow to Roberts who, since becoming chief justice in 2005, has watched in dismay as the court becomes increasingly politicized and suffers an erosion of public trust.

It suffered a huge setback when Mitch McConnell, then the Republican majority leader in the Senate, refused to grant a hearing to Barack Obama’s nominee for the court, Merrick Garland.

Donald Trump appointed three supreme court justices, with Kavanaugh’s hearings particularly contentious. It recently emerged that Ginni Thomas, the wife of Justice Clarence Thomas, had urged Trump’s chief of staff to overturn the 2020 presidential election result.

Now comes the political and societal earthquake of Roe v Wade. Scotus Blog, a widely respected law blog, tweeted: “It’s impossible to overstate the earthquake this will cause inside the court, in terms of the destruction of trust among the Justices and staff. This leak is the gravest, most unforgivable sin.”

Carl Tobias, a law professor at the University of Richmond in Virginia, said: “Chief Justice Roberts is probably beside himself. He has no idea how badly this could damage what he cares about most: reputation

“Everybody knows that the court depends on public opinion for enforcement. It doesn’t have the purse or the sword and so it must lead in terms of the highest ethical standards and this promises to disrupt that in a period when there’s substantial distrust of the court already.”

An opinion poll by Gallup last year showed just 40% of Americans approve of the job the supreme court is doing – the lowest share since the survey began in 2000. A new high of 37% said court is too conservative.

Tobias added: “This is a bombshell on top of that. Roberts will do what he can but I don’t know what that would entail.”

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