There are reasons to be pessimistic, and little grounds for optimism: The Dems have NO reliable majority in the Senate. "Independent Senator" Loserman will inevitably and invariably side with the Regime in any such battles as those one might envision between the Unitary (Unitard?) Executive (of which he is a staunch advocate) and the checks-n-balances Congress. Maybe there are one or two true 'conservatives' among the GOPukes--Grassley? Hagel?--who might object, but the number is vanishingly small and the chances of defections among the Pukes are also vanishingly small.
In addition, the Dems' majority in the House is smaller than the number of BlueDog Dems there are still sitting there, whose allegieance to the Party is evanescent, to say the least; to say nothing of the resolutely 'centrist' tendencies of the leading lights (Lites) of the DLC. So tthey cannot expect much help there, especially if the "I" word surfaces as a consequence of the investigations.
Then there is the proudly and profoundly GOPuke Supreme Court. Roberts, Scalito, and Thomas already comprise a bloc ready to uphold the fascist Busheviks' claims to total executive privilege and the Unitary Executive, and Kennedy doesn't--and never will--have the stones to oppose the Opus Dei boys on such matters.
So it seems likely to me that, if a Constitutional crisis were to ensue from Bushevik obstinacy in the face of legitemate subpoenas, the fascist Bushistas have little to fear from Congress, less to fear from the lap-dog *SCUM*, and nothing at all to fear from an apathetic, lazy, fat, and complacent populace.
But mebbe that's just me?
*SCUM*: So-Called Unbiased Media