Chris

Not entirely true. The Supreme Court’s rulings become precedent without then requiring legislation or constitutional amendment. Granted the court is interpreting the constitution in specific circumstances but their rulings can and do permanently alter the way public life is conducted. (Roe v Wade is a historic example which determined a woman’s basic right under the constitution to have an abortion). Lower courts’ rulings may set precedent or be regarded as ‘persuasive’ in subsequent cases.

I think what’s at issue here is what we in the UK would understand as convention rather than precedent. We often do stuff in government because that’s how it has been done before, and it is widely regarded as politically difficult (though not illegal) to behave differently without good cause. Giving parliament a vote on military involvement in Syria is a good example of this. Even though it was only done once, hard questions will be asked if the government moves to deploy armed forces to a foreign battlefield in future, without asking parliament first.

I suspect - though I don’t know for sure - that what’s at play in the US right now is similar to our unwritten system of convention rather than the legal process we would call precedent. Trump’s opponents are pointing out that he is not behaving conventionally. It’s not a legal claim, but a political one, which in the middle of an election campaign, seems a perfectly reasonable course of action.