The saga of judge Brett Kavanaugh’s confirmation to the supreme court is over, and it is time for the credits to roll. Top billing will go to a Republican president and his allies in the Senate who were willing to allow norms to be steamrollered and justice to be short-changed in the pursuit of a reliable conservative majority on the court. But the greatest cost of all for Republican ambition will be paid by the supreme court in its most precious coin: legitimacy.

The court may soon face cases on matters such as whether a sitting president can be charged with obstruction of justice

The supreme court can enable or block sweeping changes in US life. The court’s legitimacy as it does so rests on the public’s faith that its decisions can cut both ways. At a time when partisanship filters public perception of nearly everything that happens in political life, the supreme court retains an aura of non-partisan rectitude that the other branches of government long ago squandered. Just as we accept losing democratic elections because we know we could win the next one, the supreme court has weathered unpopular decisions because even disaffected groups retained faith that the long arc of justice would eventually bend back in their direction.

Yet now, the winner-take-all approach to the court adopted by Republicans is threatening this perception by making it appear that the court is being weaponized to serve one party. First, Republicans purloined a seat for Neil Gorsuch by refusing to consider Barack Obama’s pick for a vacant seat on the court in 2016.

Play Video 3:24 Key moments from Brett Kavanaugh's confirmation battle – video report

Then, during Kavanaugh’s confirmation hearings, Republicans have claimed to hear and see no evil as their nominee shed any pretence of impartiality and raved about a conspiracy to block his confirmation by “leftwing opposition groups” and those angry “about President Trump and the 2016 election”. Careful to namecheck every Republican bete noire and placate the watching president, Kavanaugh even invoked the Clintons. Never before has a judge sought a seat on the supreme court with such a stunning declaration of political war – a war against groups who may one day bring cases before the very court on which he aspires to sit.

Two potential disasters loom as a result. The first is that the court votes with a narrow majority to protect Trump or his associates from law enforcement. The court may soon face cases on fraught constitutional matters such as whether a sitting president can be charged with obstruction of justice, the extent of the presidential pardon power, and whether a sitting president can be indicted at all. The Gorsuch affair, combined with Kavanaugh’s blatant partisanship and sycophancy to Trump in his confirmation hearing, could create something close to a constitutional crisis if the court votes to protect the president from due process of law. The damage to the court’s image, not to mention US democracy more broadly, would be profound.

The second challenge will unfold more slowly over the decades for which a conservative majority on the court is likely to now be assured. The court could revisit decisions on reproductive rights such as Roe v Wade or Planned Parenthood v Casey, or accelerate the weakening of voting rights that was enabled by Shelby County v Holder. The spectacle of Americans having popular rights stripped away by a court whose majority was born in such partisan circumstances is likely to profoundly affect its perception among the public.

A public loss of faith in the courts as they become weaponized in the service of a particular agenda is a hallmark of authoritarian and illiberal regimes. Courts in such countries also typically act to shield the autocrat and his political allies, enabling their further accumulation of power. A supreme court majority born under these circumstances, which protected Trump from the law and enabled gerrymandering and voting restrictions that benefited Republicans, would hasten the movement of Trump’s US into the same camp as Erdoğan’s Turkey and Orbán’s Hungary. By consolidating Republican power, it would also make breaking camp and heading back towards the light that much more difficult.

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Proposed Democratic solutions – such as packing the court with additional liberal judges to redress the balance – risk creating a spiralling conflict that does nothing to restore the court’s legitimacy as a non-partisan institution. Republicans are hence setting in motion a partisan conflict that, like so many others in recent US history, will leave the country’s democratic institutions dangerously weakened. Just as fake news thrives on creating a false equivalence between its own lies and the truth, the forces of authoritarianism and division in US political life will be strengthened if they can drag the court down to their own level.

Republican senators who still care about the ideals of the US’s founding and the strength of its democracy, ought to have thought carefully about these risks before they voted in Kavanaugh. They might have won the court, but they risk losing their nation in the process.

• Andrew Gawthorpe is a lecturer in history and international studies at Leiden University in the Netherlands

• This article was amended on 11 October 2018 to clarify that Republicans refused to consider – as opposed to confirm, as stated in an earlier version – Obama’s pick for a vacant seat on the court in 2016.

