The term for this is extortion.

The last time tariffs were this high, it led to rampant corruption as companies would pay off customs officers. This was one of the reasons for switching to an income tax. For the current administration this possibility counts as a major opportunity to generate personal wealth.

But this isn't the only reason for the policy. For someone who is at heart a coward, bullying and brandishing raw power over others is its own reward. That reason enough for the policy, and damn the consequences for the nation.