So they would be unable to increase their tariffs?
No. They could increase them.
Imports to the USA amount to about 3 trillion a year, virtually all of it duty free. A 10% tariff would balance the budget( if gov spending returned to 2008 levels ) and stop the devaluation ( “quantitative easing” ) of the US Dollar immediately. That is just the financial effect, it also would incentivize US manufactures to upgrade older US factories instead of off shoring. It would slow the halt of the suicidal de industrialization that is going on in the USA.