Until now, the Barack Obama re-election campaign has focused its rhetorical guns almost exclusively on Mitt Romney.  The Wall Street Journal reports that may soon change, however.  With Rick Santorum soaring at least for now to the top of the polls, they will begin adding him to their messaging hit list:

President Barack Obama’s re-election campaign has begun discussing whether to attack Republican presidential candidate Rick Santorum and try to define him for a general-election audience, potentially breaking from its focus on Mitt Romney.

Obama campaign aides are stepping up their examination of Mr. Santorum’s record to assess his vulnerabilities and consider how their strategy might change if he becomes the GOP nominee.

For example, the Obama campaign has criticized Mr. Romney for shifting his policy stances and painted him as out of touch with middle-class Americans. That line of attack might not prove as effective against Mr. Santorum, who Obama advisers believe has gained ground in the nominating contest by looking more genuine and empathic to voters than Mr. Romney. …

But after Mr. Santorum’s surprise victory in Colorado, Missouri and Minnesota last week, Obama campaign aides have been rethinking whether a Romney-centric approach still makes sense, campaign advisers said Thursday.

While other Republicans, notably Newt Gingrich, have risen to challenge Mr. Romney in recent months, Mr. Santorum looks to be a candidate whose appeal isn’t about to fade, they said.

In fact, Santorum’s rise seems to have caught Team Hopenchange a little flat-footed.  How else to explain this weird e-mail bleg to its supporters in Pennsylvania, trolling for dirt in the Keystone State?

The campaign sent an e-mail asking Obama’s Keystone State supporters to submit their most damning “recollections” of Santorum, who served as a congressman and a senator from Pennsylvania for 16 years before losing reelection in 2006.

Santorum became a favorite target of liberals with his passionate statements against homosexuality and abortion, but despite his deeply conservative take on social issues, he has shown some ability to connect with blue-collar voters in the GOP presidential race — voters who have been a hard sell for former Massachusetts governor Mitt Romney and could be crucial in a general election.

“Folks across the country are just starting to learn about Rick Santorum as he enjoys his newfound wave of popularity,” says the note, which was signed by Bill Hyers, Pennsylvania state director for Obama for America. “But people here have known him for some time. . . . And it’s on us to make sure the rest of the country sees Rick Santorum’s true colors.”

Will they start asking the “bitter clingers” in Pennsylvania, too?  Team Obama seems very worried about that blue-collar vote, and they should be, especially in PA, to whom that “bitter clinger” remark was directed in 2008.  Hillary Clinton beat Obama in Pennsylvania and Ohio by winning that demographic, and Santorum would be better positioned than Romney to do the same in a general election.  Obama cannot win the White House if he loses both states in November, plus Indiana and possibly Wisconsin, where he’s already in trouble.

Meanwhile, the Santorum campaign just sent out an e-mail informing the media of a “major campaign announcement” in Ohio at 2 pm ET:

Republican Presidential Candidate Rick Santorum will make a major campaign announcement this afternoon at the Ohio State House in Columbus, OH. All media are encouraged to attend.

I’d guess that Santorum picked up a major endorsement — perhaps Governor John Kasich.  Don’t forget that Mitt Romney fumbled his statement of support for Kasich’s controversial PEU reforms last year, although he did end up making it very clear that he backed Kasich.  If Kasich backs Santorum, that may go a long way towards rebutting Romney’s attacks on his campaign for being the candidate of Big Labor, which Santorum has vehemently disputed.  If it’s not Kasich, it had better be someone significant like Senator Rob Portman or a figure of state-wide stature.

Update: It may not be Kasich, who has been neutral so far, but a switcher instead, according to BuzzFeed:

A top Ohio supporter of Governor Mitt Romney will switch sides and endorse Rick Santorum in Columbus this afternoon, a campaign source said. …

While Ohio Gov. John Kasich remains neutral, Romney has the support of a handful of top current and former Ohio officials, including Attorney General Mike DeWine, Rep. Jim Renacci, and former Senator George Voinovich.

Voinovich is more center-right than conservative, which would actually play in Santorum’s favor.  A switcher always has some impact, but we’ll see soon enough how significant the endorser is.  Also, I wrote “Pat Toomey” when I meant Rob Portman, and I’ve corrected it above.

Update II: Maggie Haberman at Politico guesses it’s DeWine:

DeWine and Santorum have a relationship dating back to their days in the Senate, which is why he would be the likeliest of the group. If that does prove true, it will be a huge boost to Santorum, and another very hard-to-spin headline for Romney.

If it’s someone with statewide standing, she’s right — it will add to a sense of momentum in Ohio that’s already gone Santorum’s way for the last two weeks.

Update III: WaPo reporter Dan Balz says that a “knowledgeable GOP strategist” says it’s DeWine, switching away from Romney.  It’s a big deal, in part because of DeWine’s standing in the state, and in part because he’d been seen as a more moderate Republican in Ohio (like Voinovich).  Santorum could use that as an argument that he has a better electability quotient than Romney, and the momentum will reinforce that message.