Three months ago, Marco Rubio tried to use the story of Trump University to cut down his primary rival. "He's trying to do to the American people what he did to people in this course," Rubio said in a debate, attempting to turn the case into a metaphor for the entire Trump candidacy. "He's trying to con people into giving him their vote just like he conned these people into giving him their money." But as you might recall, it didn't work — Trump kept rolling, right over Rubio and right to the Republican nomination.

But as you read this, there is probably a focus group in progress somewhere, in which undecided voters are being shown documents from the Trump University lawsuit and asked for their reaction while Democratic pollsters and media consultants watch eagerly from behind one-way glass, convinced this could be the attack from which Trump cannot recover. And they might be right.

What changed? The vague and somewhat abstract became concrete, in the form of documents from a class-action lawsuit against Trump, in which former marks — pardon me, students — of Trump U are suing the Republican standard-bearer for fraud. Now that the documents have been publicly released, instead of general characterizations of what went on there, we have former employees testifying about how they were instructed to encourage the students to max out their credit cards, how they used the students' desperation ("are they a single parent of three children that may need money for food?") as a tool to manipulate them into making ever-larger purchases of the supposedly life-changing seminars, or how one Trump U salesman was reprimanded after he failed to push a struggling couple to sign up for a $35,000 package because he knew they couldn't afford it (unfortunately for them, another salesman stepped in and closed the sale).

Any political consultant will tell you that if you want to say your opponent lied or call him a hypocrite, it's much more effective if you've got his actual words — and it's even better if they're on tape. The more concrete the evidence, the harder it is to ignore or explain away. That's what these Trump University documents do: not just recast this particular tale, but allow Democrats to make it a metaphor for Trump's candidacy, just as Rubio tried and failed to do.

Trump's wealth has represented any number of things to voters up until now. To many of his supporters, his plane and resorts and spectacularly gold-plated apartment (done up in a style we might call Late Russian Mobster) represent success, proof of Trump's competence and skill. To many others, his wealth represents Trump's shallow and classless venality. But for the most part, until now it was essentially harmless and amusing. That's in contrast to the last person the Republicans nominated for president, who seemed to always be apologizing for his wealth — the last thing Trump would ever do.

Democrats successfully convinced voters that Mitt Romney was a heartless corporate raider who would step over his own mother to make another million. They had any number of grounds on which to make that case, but none was as powerful as the stories of people who had been laid off by a company Romney's Bain Capital had bought. In one devastating super PAC ad, a worker in an Indiana factory told how he and his coworkers were instructed to build a stage in their plant; the stage was then mounted by executives who told the gathered workers that the plant was closing and they were all going to lose their jobs. "Turns out that when we built that stage, it was like building my own coffin," said a man in the ad.

But Trump's wealth had never seemed to come at anyone's expense. Sure, you might think Trump Tower is a monument to '80s garishness, but no one's being forced to buy an apartment there. Trump Steaks might have been a joke, but at worst you were one of the tiny number of people who bought some on a trip to Sharper Image, ate them, and chose not to become a repeat customer. Victims were few and far between.

That is, until Trump University. Now Democrats can say that not only is Trump a fraud, he's a con artist who destroys people's lives in order to buy himself a new hair weave. That recasts Trump's wealth, which has always been his primary qualification for office. The absurd notion that is President Donald Trump rests on the idea that as a successful businessman, he knows how to get things done and make things work. It's much harder to believe if you associate him less with titans of industry and more with the guys running three-card-monte games in the shadow of one of his buildings.

All that isn't to say that the emerging attack on Trump U is guaranteed to work. Even if Democrats decide to make it the centerpiece of their campaign against Trump, it will be only one piece of a very complicated puzzle. But now that they have a vivid, concrete way to make the case, its chances of success are much higher.