Just saw this and I was wondering if it was a legit quote. I've seen similar claims about Biden too, here the PolicyMic headline statesPolicyMic headline states "Joe Biden Wanted Bush Impeached For the Very Thing Obama is About to Do".
The above graphic reads,
The Founding Fathers were, as in most things, profoundly right. That's why I want to be very clear: if the President takes us to [war] without Congressional approval, I will call for his impeachment.
I do not say this lightly or to be provocative. I am dead serious. I have chaired the Senate Judiciary Committee. I still teach constitutional law. I've consulted with leading constitutional scholars. The Constitution is clear. And so am I.
- Joe Biden, 2007