If there is one word that sums up the Obama campaign’s strategy in attacking Mitt Romney’s economic credentials, it’s this: “risk.”

Risk is the theme that runs through the two key interwoven themes that the Obama team is trying to establish with its storytelling about Romney, Bain, and the middle class.

It’s often assumed that attacks on Bain are about hitting Romney’s wealth and character. But they are about something larger: about sowing doubts and fears among swing voters about Romney’s vision of our economic future. By invoking a Bain deal in which executives made millions while the bottom fell out from under workers, the Obama team is painting a vision of an economy under President Romney that’s built on a flimsy foundation of unbridled corporate profiteering and risk-taking — the same type of Wall Street recklessness that led to the crisis and untold economic suffering. That’s one way “risk” is a key theme.

The second way “risk” is central to the Obama strategy will be related: changing leadership right now is too risky a gamble with the recovery, which is underway but remains fragile — an argument you’ll be hearing more of soon enough. The basic problem for Obama is that while economic confidence is rising, Americans remain unhappy with his stewardship of the economy, and appear open to Romney’s argument that his success in turning around troubled companies equips him to turn around an entire country faster than Obama has.

Obama needs to persuade Americans that the current recovery, while unacceptably slow, is moving us towards a secure economic future (hence the slogan “an economy built to last”), and that Romney’s aura of economic competence is basically a ruse. It masks the fact that Romney’s actual policies, priorities, and ideas about the economy would represent a backward lurch that would line the pockets of the very rich but imperil and upend progress for the rest of us. That’s also key to attacks on Romney’s secrecy on tax returns, offshoring, big bundlers, and what government program’s he’d cut. Risky.

The message: Obama = long term economic security based on a strong middle class. Romney = a risky gamble for everyone but the very rich, and more middle class insecurity.

* Joe Biden to assail Romney over Bain: The above is key to understanding the political goal of the remarks Joe Biden will make today, which will focus (again) on GST Steel and the hundreds of workers laid off there:

The top 30 executives walked away with $9 million. And Romney and his partners walked away with at least $12 million. Romney made sure the guys on top got to play by a separate set of rules, he ran massive debts, and the middle class lost. And folks, he thinks this experience will help our economy?

Where I come from, past is prologue. So what do you think he’ll do as President?

* Outside money begins flowing from the right: Here we go: The Rove-founded Crossroads is launching a $25 million ad campaign in 10 states bashing Obama over the economy, and contrasting his promises on foreclosures and the deficit with what will surely be a very lurid picture of today’s economic landscape (the ad itself isn’t available yet).

The new Crossroads campaign is at least six times larger than the $4 million in ads launched yesterday by the pro-Obama Priorities USA action, illustrating again that conservatives will dominate in the outside money ad wars.

* Obama campaign raises over $40 million in April: The Obama campaign announces in a new Web video that it has raised $43 million in April, in average donations of around $50. Obama’s big (current) cash advantage over Romney means it will be left to the campaign to mostly wage the air battle with conservative outside groups, particularly since some counterparts on the left are investing heavily in on-the-ground organizing instead.

* Rove’s group matches Obama campaign in spending: Perfect illustration of the above, from Zeke Miller: Crossroads’ planned $25 million ad buy for the next month represents “the same amount the Obama campaign has pledged to spend in May.”

There you have it. The difference, of course, is that in Obama’s case, we know who the donors are, and Obama himself is accountable for the ad’s message.

* Bush gives Romney’s amnesia strategy a big assist: Karen Tumulty confirms that the Romney campaign doesn’t want, er, expect George W. Bush to be doing any campaigning on Romney’s behalf this year. This will give a big lift to Romney’s goal of lulling Americans into mass amnesia about the circumstances Obama inherited upon taking office — not to mention mass amnesia about Bush’s policies and the similarities between them and Romney’s.

* Could campaign finance free for all cost GOP a Senate seat? Jonathan Bernstein opined yesterday that a surprise win by Deb Fischer (who enjoyed a big influx of cash from one donor) in the Nebraska Senate race should raise new questions about the rollback of campaign finance limits and the ability of single donors to effectively buy Senators.

Well, Fischer won, and will now be facing Bob Kerrey in the general.

* GOP chance at controlling Senate slipping away? Steve Kornacki on Fischer’s surprise win yesterday, the overall Senate map, and the possibility that GOP primary voters could end up costing their party control of the Upper Chamber.

Historical footnote: GOP primary voters may have cost Republicans Senate seats in Delaware (see O’Donnell, Christine) and Nevada (see Angle, Sharron).

* Elizabeth Warren gets back to basics: Her campaign is up with a new ad featuring working class Massachusetts residents describing her as a fighter for their interests who’s not afraid to take on the big banks.

The closing description of her as “the real deal” seems like a rebuff to ongoing GOP efforts to sow doubts about her bio and character. The ad, and a Boston Globe article she’s published calling for more Wall Street reform after the J.P. Morgan debacle, is a reminder that Warren needs to get the race back to what she had always hoped it would be about.

* The stealth campaign of conservative judicial activists: Forget Obamacare: Jeffrey Rosen sounds the alarm over another conservative judicial assault that could have far reaching consequences for the right’s attacks on federal regulation.

* And Obama not paying any price over gay marriage: Via Taegan Goddard, a Reuters poll finds that the percentage of Americans who view Obama favorably or unfavorably in the wake of the announcement is almost exactly even, at around 30 percent, while 40 percent say it made no difference. Among independents, that number is 54 percent, suggesting, again, that this “risky move” is a wash at best.

ICYMI: Polling shows that Obama is unlikely to pay any price for the announcement even in the swing states.

What else?