Democrats have been increasingly frustrated that not even an army of fact-checkers has been able shame the Romney-Ryan campaign from stopping their lies about Medicare savings, welfare requirements, the Janesville GM plant and more.
The shamelessness is unlikely to abate. But Bill Clinton may make them pay a steep price. 
Part of what makes Clinton a unique figure in American politics is that the camera stays on him longer. Most politicians get cut off trying to explain things, but never Clinton. And he uses that to his advantage.
Last night, he used it to debunk the lies. 
Look, here’s what really happened. You be the judge. ... There were no cuts to benefits at all. None. What the president did was to save money by taking the recommendations of a commission of professionals to cut unwarranted subsidies to providers and insurance companies that were not making people healthier and were not necessary to get the providers to provide the service.
And instead of raiding Medicare, he used the savings to close the doughnut hole in the Medicare drug program ... and to add eight years to the life of the Medicare trust fund so it is solvent till 2024. So President Obama and the Democrats didn’t weaken Medicare; they strengthened Medicare.
Now, when Congressman Ryan looked into that TV camera and attacked President Obama’s Medicare savings as, quote, the biggest, coldest power play, I didn’t know whether to laugh or cry, because that $716 billion is exactly, to the dollar, the same amount of Medicare savings that he has in his own budget.
It takes some brass to attack a guy for doing what you did.
And he easily put to rest the Obama Gutted Clinton's Welfare Reform Lie: 
Let’s look at the other big charge the Republicans made. It’s a real doozy. They actually have charged and run ads saying that President Obama wants to weaken the work requirements in the welfare reform bill I signed that moved millions of people from welfare to work ... you need to know, here’s what happened. Nobody ever tells you what really happened — here’s what happened.
When some Republican governors asked if they could have waivers to try new ways to put people on welfare back to work, the Obama administration listened because we all know it’s hard for even people with good work histories to get jobs today. So moving folks from welfare to work is a real challenge.
And the administration agreed to give waivers to those governors and others only if they had a credible plan to increase employment by 20 percent, and they could keep the waivers only if they did increase employment. Now, did I make myself clear? The requirement was for more work, not less.
So this is personal to me. We moved millions of people off welfare. It was one of the reasons that in the eight years I was president, we had a hundred times as many people move out of poverty into the middle class than happened under the previous 12 years, a hundred times as many. It’s a big deal. But I am telling you the claim that President Obama weakened welfare reform’s work requirement is just not true.
Maybe Mitt, you shouldn't have featured Bill Clinton in that welfare ad. 
And Clinton brought up the very truthful comment recently uttered by Romney's pollster:
...they keep on running the ads claiming it. You want to know why? Their campaign pollster said, we are not going to let our campaign be dictated by fact-checkers. Now, finally I can say, that is true. I couldn’t have said it better myself.
And I hope you and every American within the sound of my voice remembers it every time they see one of those ads, and it turns into an ad to re-elect Barack Obama...
Clinton hopes to be the ultimate referee, so deeply wounding the Romney-Ryan credibility that any false charge they launch in the homestretch of the campaign gets dismissed out of hand.
Was it enough to restore the boundaries of decency and end the "post-truth" campaign? I can't predict if the media will step up their truth-squadding, or how much voters will take notice.
But short of a killer retort in the upcoming debates, Clinton exploiting his outsized platform was as big a shot as Democrats could fire.