From reason:

The administration’s claim that a near-categorical ban on work visas is necessary to help American workers is at odds with numerous analyses by economists (which show that immigration restrictions do as much to reduce native-born employment as increase it, even during times of crisis such as the Great Depression), and with evidence indicating that immigrant students (severely restricted by the ban on new J-1 visas) and high tech workers are especially crucial to American innovation, which in turn helps facilitate economic growth. Caleb Watney of the conservative R Street Institute recently summarized that evidence here.