The most important number in the new NBC/WSJ poll may be this one:

How much would you say you know about Mitt Romney and what he stands for — a lot, a fair amount, just some, or very little?

Know a lot: 20

Know a fair amount: 46

Know just some: 22

Know very little: 12

Only one-fifth of Americans say they know Romney very well, and it’s save to assume the 46 percent who say they know a fair amount may be overstated. This is what the Obama campaign’s attack on Romney’s Bain years is about — it’s a race to define Romney before he can define himself. Romney is asking voters to see him as an energetic figure who has done exceptionally well for himself and is now poised to use the skills he acquired in the private sector to break the country out of its rut. Where Obama has proven weak and ineffective, Romney can jolt the economy to life and can break the stalemate in Congress.

The Obama camp, meanwhile, hopes to cement an image of Romney as the rich guy who has done fabuously well for himself and now thinks running the country would make a diverting — and easy — next move. Romney, in this telling, is the guy who got obscenely rich while the floor fell out from under the middle class. Why would that equip him to create jobs or fight for you? This guy has never really been on your side.

Or, as Jonathan Chait put it, the Obama team wants to “define his motives and perspective: a rich man who sees the world from the perspective of the CEO suite and blithely assumes what is good for people like himself is good for everybody.”

The NBC/WSJ poll also tested the efficacy of the attacks on Bain:

Has what you have seen, read, or heard about Mitt Romney’s previous business experience managing a firm that specializes in buying, restructuring, and selling companies made you feel more positive or more negative about him, not made much difference in your opinion or do you not know enough about this to have an opinion at this time?

More positive: 23

More negative: 28

Not much difference: 24

Don’t know enough: 24

Note those last two numbers: Nearly half the voters are not moved one way or the other by Romney’s business experience or don’t know enough about it to form any opinion. Yet for both sides, the argument over the meaning of Romney’s background is absolutely central. Which is to say that in the race to define Romney, both sides still have an enormous amount of work to do.

* Is Romney on the defensive over Bain? Christian Heinze suggests watching to see if the attacks on Bain reorient Romney’s Veep search towards pols (such as T-Paw) who might better connect with blue collar in the Rust Belt, where offshoring remains a potent issue.

* People want government to do more, not less: One other key number in the NBC/WSJ poll: A plurality, 49 percent, think that “government should do more to solve problems and help meet the needs of people.” By contrast, 47 percent say that “government is doing too many things better left to businesses and individuals.”

This is the turf that the election is being fought on, and as always, while people say they favor cutting government spending in the abstract, in reality attitudes towards government are complex, in flux, and not easy to pin down.

* Obama leading in three key swing states: A new Quinnipiac poll finds Obama leading Romney in Ohio by nine (47-38); in Pennsylvania by six (45-39); and in Florida by four (45-41).

The lead in Ohio is particularly striking. He leads among independents by 45-36. And he is more trusted on the economy by 47-42; given that Ohio is probably a must-win for Romney, it’s worth recalling that he opposed the auto-bailout, which led to a resurgent auto industry in the state.

* Why Dems are avoiding the Dem convention: With the press seemingly obsessed with which Dems are and aren’t going to the convention, Alex Roarty cuts through the noise and explains that Dem officials don’t see this as a problem, because it’s all rooted in demographics.

“Obama’s campaign has targeted a combination of minorities and white-collar whites, particularly women, to win a majority of the election,” Roarty notes. “That could be a winning strategy for him, but it’s unworkable” for the Dems who will be no-shows, who are from “culturally conservative regions” where constitutents are “overwhelmingly blue-collar — a group that has soured on Obama.”

* White House, GOP fail to reach deal on Holder: Ed O’Keefe and Sari Horwitz have the scoop: White House officials offered to hand over some of the documents Darrell Issa is requesting in the Fast and Furious scandal, in exchange for Republicans permanently dropping plans for a vote to hold Eric Holder in contempt. Republicans declined.

And so the vote will proceed tomorrow. If the Supreme Court nixes all or parts of Obamacare, and Holder gets held in contempt, it will be a very rough day politically for the White House.

* How many Dems will hold Holder in contempt? Dem Rep. Jim Matheson of Utah becomes the first Dem to announce that he will vote to hold the Attorney General in contempt during tomorrow’s vote in the House of Representatives. Keep an eye on the defecting Dems over the next 48 hours — voting against Holder will likely be seen by vulnerable Dems as a way of displaying “independence” from the administration.

* The “lies” at the center of Fast and Furious: Fortune undertakes a massive investigation into the Fast and Furious scandal, and concludes that the core allegations are “replete with distortions, errors, partial truths, and even some outright lies.”You don’t say!

* Tom Perriello on “communitarianism”: Former Congressman Tom Perriello, who won national attention for defending the health law amid his 2010 loss, has a nice piece on E.J. Dionne’s new book on communitarianism and the need for liberals to take back American history and values from the Tea Party.

* And EPA’s climate rules are upheld in court: Brad Plumer on a new federal court ruling that the EPA was “unambiguously correct” in limiting greenhouse gas emissions, why that’s a setback for big polluters, and why the decision could be just as important as SCOTUS’s Obamacare decision tomorrow.

Or, as Kate Sheppard put it: “Turns out the Obama Environmental Protection Agency didn’t make up all that stuff about carbon dioxide being bad for you.” Bad day for the climate cranks....

What else?