Rick Santorum's exit from the GOP primary race means the super PAC money that kept his presidential bid alive will now likely be spent on anti-Obama attack ads. - 

David Brancaccio: With Rick Santorum's exit from the Republican presidential contest, political analysts say the general election is beginning in earnest.

Marketplace's Bob Moon has the latest on big political action committees -- you may know them as super PACs -- and their ongoing role in the race.

Bob Moon: You can expect to start seeing more anti-Obama attack ads in the near future, now that the Romney campaign and Republican-aligned super PACs can redirect their advertising fire.

John Dunbar watches politics at the Center for Public Integrity.

John Dunbar: Restore Our Future, which is a super PAC backing Mitt Romney, actually has more money in the bank than Mitt Romney's own campaign, or at least it did at the end of February.

Up to now, that super PAC has been doing most of its spending -- roughly $40 million -- on negative ads targeting his GOP rivals. But at the PoliticalWire website, Taegan Goddard says other super PACs were busy helping Romney's rivals extend their improbable runs.

Taegan Goddard: I think what happened is, the super PACs allowed the unorganized candidates like Rick Santorum and Newt Gingrich to continue on longer than they otherwise would have been able to.

Now, Dunbar says all those super PACs can start banding together.

Dunbar: They've obviously got a horse they can back without reservation -- they don't have to worry about Rick Santorum anymore. Now they can just go straight at Barack Obama.

The bulk of the spending is likely to be focused on a dozen-plus so-called battleground states, considered key to a November victory.

I'm Bob Moon for Marketplace.