Feingold, who championed campaign finance reform in the 1990s, used most of his address to attack Citzens United, the 2010 Supreme Court ruling that has paved the way for direct, unlimited corporate involvement in elections.
Republicans have used the new rules to pump millions in untraceable funds into elections. President Obama has attacked the ruling, and Democrats have sought to make it a campaign issue. At the same time, Priorities USA seeks to level the financial playing field by engaging in the same sort of anonymous unlimited spending the Democrats publicly deride.
This is a mistake, Feingold said.
"We'll gut our message!" he exclaimed. "I don't just think it's wrong, I think it's a dumb strategy."
"We can raise that money with people power," he continued. "[We can] raise it without selling our soul."
If Democrats play by the Republicans' rules, he said, "People will see us as weak. People will see us as Corporate Lite."
"It's a game we will never win," he added. "We will not win."
Late update: Here's video of Feingold's keynote speech: