Story highlights Tape catches Mitch McConnell talking to a summit run by top GOP donors

What he said to the Koch brothers is used by Democrat campaigning against him

But, Dana Bash notes, he has said the same things publicly many times

A secret audio recording of their biggest election year target -- Sen. Mitch McConnell -- talking to a donor summit arranged by the Koch brothers, the Democrats' 2014 bogeymen.

Democrats pushed "The Nation" story around online with frenetic glee.

McConnell's Democratic challenger for his Kentucky seat, Alison Lundergan Grimes, couldn't wait to whack him on it, telling CNN in an exclusive interview that "Mitch McConnell got caught in his 47% Mitt Romney moment."

"I think it shows the extent and the lengths he will go to to pander to his party millionaires and billionaires at the expense of hurting Kentuckians," Grimes told CNN.

The problem with the Democrats' argument is that Romney's 47% moment was only a moment because he was saying to donors in private something he would never have dared to utter in public:

"Forty-seven percent who are with him, who are dependent upon government, who believe that they are victims, who believe that government has a responsibility to care for them, who believe that they are entitled to health care, to food, to housing, to you name it. That that's an entitlement," Romney said behind closed doors about President Obama's supporters in 2012.

But unlike Romney, what McConnell said to the Koch brothers are things he has said in public, and more importantly, his comments mirror positions he has publicly backed with actual Senate votes: opposition to Democrats' plans to increase the minimum wage, extend unemployment insurance and make student loans more affordable through the tax system.

If Republicans are in charge, he said, those won't be coming back to the Senate floor.

"We're not going to be debating all these gosh-darn proposals," McConnell told the Koch brothers and the rest of the room full of billionaire donors.

McConnell also talked about plans, if he becomes Senate majority leader, to attach policy riders to spending bills that would defund regulations President Obama has put in place that Republicans loathe.

"I didn't say anything in the private meeting I haven't said publicly," McConnell told CNN in another exclusive interview, saying he stands by his comments.

When I put that reality to Grimes, she didn't back down on her attack. In fact she doubled down.

"I think this recording is alarming. He has promised further gridlock if elected but this is action he will directly take at the expense of Kentuckians," Grimes said.

A little context is in order for why Democrats are jumping on this like a fatal pre-Labor Day surprise:

First, it's all about the Koch brothers.

Democrats believe, based on internal polling, that voters think the system is rigged against them and that's why they're struggling.

The Democratic strategy in all the key races for control of the Senate is for the billionaire Koch brothers to become the poster boys for the rigged system -- that they pour tens of millions into the system to help Republicans, so Republicans help keep them rich.

Given that, having a muffled audio recording of the Senate GOP leader addressing those fat cats, whether he is saying anything new or not, is in fact politically beneficial to Democrats. It helps perpetuate the narrative they believe has legs.

The fact that McConnell vowed no more debate on Democrats "gosh-darn proposals" also gives Grimes an opening on another key argument against McConnell: that he is the personification of gridlock in Washington. Elect him, and it will only get worse.

The downside for Democrats is that they're not exactly clean when it comes to taking billionaire cash. They, too, have high-rolling donors pouring unlimited dollars into the system on behalf of Democrats.

But make no mistake about it: This secret audio recording will be front and center in Grimes' campaign and others for the near future.

Whether it will foment anti-McConnell fever here will depend in large part on how much is really already lying beneath the surface in this neck-and-neck race.