During the campaign for the midterm elections, we’ve heard some seriously incendiary rhetoric from Republican leaders, including Donald Trump, against the Democratic candidate for the senate seat of Michigan, Abdul El-Sayed.

The US president has called El-Sayed a “jihadist” and a member of the Muslim Brotherhood, a designated foreign terrorist organisation under US law.

There is no evidence to support these claims. But the nature of the US president’s remarks suggests an intent to harm El-Sayed’s reputation among Michigan voters.

In many circumstances, El-Sayed would have a strong claim for defamation in relation to these statements. But it’s unlikely that a court could consider a case against the president or other members of the federal government. This is due to the US Supreme Court’s doctrine of sovereign immunity, which bars defamation claims against federal employees.

In its most basic form, immunity means exemption from legal process. In the US legal framework, sovereign immunity is based on Crown immunity. This is a relic of English common law grounded in the principle that “the king can do no wrong”. It still exists in the UK, in that the reigning monarch cannot be sued for defamation. But the Crown – meaning the government and its servants – certainly can, under the Crown Proceedings Act of 1947.

But the US Supreme Court embraced the........

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