Yoo played a major roll in "paving the legal road to torture."
Yoo, early, before the war, was building a case, advising Alberto Gonzalez that Bush "that there are effectively no limits on the presidents authority to wage wara sweeping assertion of executive power that some constitutional scholars say goes considerably beyond any that had previously been articulated by the department."
Newsweek seems to have a good fix on the powerful role of Yoo in the Bush administration's disregard of the nation's laws and the constitution. Just do a search of the Newsweek website and you'll find dozens of references to his nefarious inputs.
Yoo has been one of the prime drafters of the theory that Bush, as president can ignore any laws, do anything he wants. He is, alone, one of the greatest threats to democracy the nation has ever faced, because his opinions have been used by the criminals in the white house as justification for their lawbreaking.
Ironically, when and if the Bush whitehouse criminals are ever brought to trial, Yoo may get off scott free, since he's been an advisor, not a perpetrator. Justice may never bring him in.
His legacy could be the end of democracy and constitutional rights and law in the USA.