Senator Ron Johnson said he hoped President Trump was making empty threats, but most in the G.O.P. cheered his warning that Iran’s “whole civilization” would be wiped out.

Members in both chambers of Congress said the president was threatening war crimes, and a growing number, questioning his mental fitness, called for his removal.

G.O.P. lawmakers who have given the Trump administration wide latitude to wage war with no congressional input are growing frustrated as officials offer little detail about ground troops, cost or timeline.