I don't have a lot of specific knowledge on this just general ideas.

We fought in Korea, without Congress declaring war, and people followed because they were still riding the tide of WW II.

We fought in Vietnam without Congress declarng war, and people learned from the past and started protesting.

Now we are again in a war that was NOT declared by Congress; but now we have all those from the Vietnam era of the age which puts then in the political trenches, and they are NOT going to let that happen AGAIN.

Impeachment - would not solve this particular problem because of the term of office coming to an end; as mentioned already, the process could not easily be completed before then. So to go that route would be more of a political manuever. Can the people of the Vietnam era generation NOT start the process? They may feel they owe it to themselves.