A threat like Biden's threat to impeach if they bomb Iran is nothing but permission drop the bombs; a declaration that
"We will not stop you." Once the bombs are dropped, the deed is done. Bush and Cheney have advanced the devastating agenda of their tiny fascist faction. That's all that matters to them.
Every time Bush and Cheney invoke unitary authoritarian power they declare their intent to willfully violate the Constitution. They've followed up that declaration by repeatedly, willfully, and publicly violating the Constitution. With each act, they write another article of impeachment against themselves and issue a challenge to Congress "We've just erased more of the Constitution. Stop us if you dare."
It really is tragic. The biggest barrier to impeachment is not the reactionary right -- it is the impeachment naysayers in our own ranks. The people who apparently believe in their own omniscience as they declare they "know" the outcome in the Senate, when it's impossible to know until Senators are forced to make a choice -- to stand with war criminals and defend the indefensible or toss them overboard (something Repubs are never reluctant to do when it suits them). We may well see the Repubs force Bush and Cheney out overnight to escape having to go on the record in support of men who have so outraged the nation. ("For the good of the Party"; to keep the White House in Republican hands; to show the nation they have the strength to stand up to Bush -- strength the Democratic leadership has so far failed to demonstrate.)
And even if a Member is sure it will be a "charge of the light brigade" they are duty-bound to act. The Congressional oath is an individual oath. Each and every Member has personal choice:
Impeachment or Impotence.
Duty or Complicity
Courage or Cowardice.