TPM said it better than I can (though I take issue with their title):
The End Of A Progressive Champion
As the Republican wave spreads across the country, it's time to say goodbye to one of the big-name progressive champions of the past 18 years: Sen. Russ Feingold (D-WI), champion of campaign finance reform and longtime opponent of the Patriot Act, has gone down in defeat against Republican businessman Ron Johnson. It marks the first time since 1986 that Republicans have won a Senate race here.
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Feingold's main legacy is the McCain-Feingold campaign finance reform law. But even here, the Washington Post noted this week, that law has been steadily worn down by the Roberts Court in a series of Supreme Court rulings, most notably the Citizens United decision that reopened the floodgates of corporate money in politics.
In addition, Feingold will be remembered as the only vote in the Senate against the Patriot Act, expanding the surveillance powers of the federal government, which was hastily passed in the wake of the 9/11 attacks in 2001. At Feingold events in 2004, he frequently told constituents that he was the only Senator to vote against the Patriot Act -- because he was the only Senator to read the Patriot Act.
He was also one of 23 senators to vote against the Iraq war.
He's one of the poorest members of the Senate and yet has returned more than $50,000 in pay raises back to the Senate.
Opposed NCLB.
He has consistently stood up for global human rights and civil rights.
The list goes on and on. He will be sorely missed as a Senator and I mourn his loss. I now look forward not to an ending but a beginning of something new for the good Senator, something that will help move this country back to sanity and, whatever it is, something great for a man who has more than earned my respect & admiration. I didn't agree with his every vote, but damn...his voting record and his record of challenging the status quo is pretty stellar in my book.