Good news ! It is against the law (i.e., illegal) for a US President to impose tariffs (on a whim or otherwise) -- a US President doing so is doing so illegally and without constitutional authority!

When the US President commits crimes as the US President, he has absolute immunity from prosecution (otherwise, he might not be emboldened to break the law) so there is no judicial recourse, but the US Congress can still see the illegal activity and impeach and remove him from office to stop the execution of illegal activity. As our representatives within the US Government, they are responsible to us to enact our legislative outcomes. It appears they have determined that the illegal activity is what we wanted, or there would be articles of impeachment for these illegal acts.

The legislative branch can of course deliberately impose tariffs at any time for the reasons you listed.