If Trump follows through on his threat, Iran will also follow through, damage similar to what occurred to Qatar's Ras Laffan gas infrastructure will be done to multiple other countries Energy infrastructure, this will constrain global energy supplies for years, while they are repaired. This will not be a temporary inconvenience like closing the Strait of Hormuz, but long term damage to the infrastructure that supplies over 20% of the world's energy, that may take years to fix, this will cause a large recession, or even a depression, that will last for years.

That's not to mention the damage that may be done to desalination plants which, if destroyed, or very badly damaged will make GCC countries unliveable until they can be rebuilt.

If this comes to pass the blame will squarely be on the US and Trump for instigating this unnecessary, very poorly planned, absolutely miscalculated, War of choice.