Eliot Spitzer was Governor of New York, former AG of New York, famous gadfly of Wall Street, and a top contender before the 2008 election to be Obama's pick for Attorney General, when it was discovered that he was paying prostitutes.
The explanation as to how this information was discovered is as follows: he paid for these "services" using a wire transfer to the madam, who had created an "anonymous" corporation to collect payments, as a convenience to her wealthy and famous clients. According to Wikipedia, "The investigation of Spitzer was reportedly initiated after North Fork Bank reported suspicious transactions to the Treasury Department's Financial Crimes Enforcement Network as required by the Bank Secrecy Act, which was enhanced by Patriot Act provisions, enacted to combat terrorist activity such as money-laundering." [1]
Every bank is required by the Patriot Act to file "Suspicious Activity Reports" regarding certain activity to FinCEN, which reports must be kept secret from the person being reported upon. SARs are typically filed electronically, and then centralized in FinCEN review centers, where patterns are analyzed and information is distributed to law enforcement personnel. Spritzer was being monitored because one of the chief criteria used in determining whether a SAR should be filed is whether an individual being monitored is a "Politically Exposed Person" or PEP (that acronym is actually used actively). [2]
In other words, by explicit provision of the Patriot Act and US DoT regulations, all financial activities of politicians must be monitored and reported on in secret by financial institutions.
Don't get me wrong, I wouldn't want the US Attorney General to be someone who frequents call girls. It was Spitzer's own self-destructiveness that created the opportunity for this take down. But you have to ask, if it weren't for his aggressive anti-Wall St. stance, would he have been targeted? Perhaps he wouldn't have been. There are certainly similar transgressions committed by less "problematic" politicians that never leak. For instance, even after the whole Spitzer hullabaloo, we don't know who any of this madam's other clients were, even though it was reported that some were famous politicos.
What's most significant here, though, is that we don't need to speculate about how this power can work to the advantage of certain interest groups.
In this case, broad-spectrum surveillance may have resulted in Eric Holder becoming AG at the height of the financial crisis, instead of the one man perhaps most qualified by experience and temperament to prosecute financial crimes, Eliot Spitzer.
[1] http://en.wikipedia.org/wiki/Eliot_Spitzer_prostitution_scan...
[2] http://www.sowal.com/bb/showthread.php/21466-Unintended-Cons...