Since the 70s, huh? The 70s when a Republican president so wantonly broke and disregarded the law that he had to resign from office to escape impeachment? Then the next Republican president pardoned him?
Or how about the 80s, when Reagan took part in an illegal war by illegally selling arms to a hostile enemy, Iran, to fund the fascist Contras decimating villages in Nicaragua? Then, of course, those responsible were pardoned by Bush I. Or how about when his Cabinet defrauded and stole from the government to give to their constituents rather than to build houses for the poor like the money was intended for? Savings and Loan?
Bush II has essentially declared that he is above the law and acted accordingly. The suspension of Habeas Corpus for US Citizens, advocacy and approval of torture, illegal and unwarranted domestic spying and wiretaps, ignoring both the Geneva Convention and US law in the treatment of prisoners of war, extraordinary rendition, etc. all show, as do statements by Bush and Cheney, that they feel they're above the laws and the president essentially has the right to do anything he wants in wartime (directly in contradiction with established laws).
This is to say nothing of all the crimes by lesser-tier Republican officials like Tom DeLay, Mark Foley, Ted Stevens, and on and on.
Now, Democratic politicians have been guilty of many crimes as well (of which Blagojevich is just one example). My point is not that it's Republicans specifically that act as though they're above the law. Rather, pretending that it's unique and pronounced in Democrats alone and not a problem of politicians across both aisles is intellectually dishonest and factually inaccurate.
Tons and tons of politicians are corrupt, unscrupulous politicians. This does not come as a result of their party affiliation, that has nothing to do with it, it comes as a result of their lack of ethics.