But the Vermont Independent appears to be fed up with niceties after a pro-Clinton super-PAC reportedly shoveled dirt on Sanders to a reporter.

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In an email to campaign supporters on Tuesday, Sanders linked Clinton to three things her campaign has been trying to disassociate itself from: Wealthy donors, dirty tactics and, yes, even the biggest boogeymen in left-wing American politics — the billionaire industrialists Charles and David Koch.

Sanders wrote in the email, "Yesterday, one of Hillary Clinton’s most prominent Super PACs attacked our campaign pretty viciously. "They suggested I’d be friendly with Middle East terrorist organizations, and even tried to link me to a dead communist dictator. "It was the kind of onslaught I expected to see from the Koch Brothers or Sheldon Adelson, and it’s the second time a billionaire Super PAC has tried to stop the momentum of the political revolution we’re building together." The pro-Clinton super-PAC Sanders is referring to is Correct the Record — an opposition research and strategy group founded by perhaps Clinton's most aggressive operative, David Brock. The story Sanders is referring to is a report by The Huffington Post that in part reads:

"A super PAC backing Democratic presidential candidate Hillary Clinton is going negative, circulating an email that yokes her chief rival Sen. Bernie Sanders (I-Vt.) to some of the more controversial remarks made by Jeremy Corbyn, the United Kingdom's new Labour Party leader, including his praise for the late Hugo Chavez, the Venezuelan leader who provided discounted fuel to Vermont in a deal supported by Sanders."

The Clinton campaign and Correct the Record have not responded to requests for comment. Correct the Record is tied especially tightly to Clinton's campaign as the two groups are exploiting a loophole in election laws that apparently allows the outside super-PAC to coordinate directly with the campaign. Sanders, who has refused to use a super-PAC, clearly sees an opening to attack Clinton, who is accepting million-dollar-plus donations to her main outside spending group Priorities USA Action while at the same time promising to reform campaign finance laws to reduce the corrupting influence of big money on the American political system. "I don’t have a Super PAC, Friend," Sanders says in the email. "I am not going to travel around the country begging millionaires and billionaires for money. That’s just not going to happen." Toward the end of the email, Sanders gets to his point: "Make the Super PACs pay for attacking us by making a $3 contribution to our campaign today. Let’s send a powerful message that we have had ENOUGH of the billionaire class buying elections.

"If we stand together to fight back against these ugly attacks, we can ensure this election is about who has the best ideas, and not who has the biggest donors."