A less obvious downside of Donald Trump’s presidency is that we might never know what will happen when the EPA’s 2025 fuel economy regulations come into force.

Read more: Donald Trump may ditch ‘onerous’ US fuel economy laws

If buyers won’t buy the cars that legislators want them to, what happens next? State laws banning certain vehicles and engine sizes?

There’s an argument that climate change regulations and the free market are on course for a huge collision.

Since the first EU CO2 laws in 1998, car makers have been using diesel to drop fleet CO2 to the planned 95g/km average in 2020/21.

However, the introduction of real-world tests for both fuel economy and tailpipe pollution could make hitting that target impossible.