GOP

Though he's been campaigning in Pennsylvania with a man at the center of running-mate speculation — Florida Sen. Marco Rubio — the likely GOP presidential nominee hasn't said much about whom he might choose. Mitt Romney's pick for vice president could help him win an important state or a key voting group.

Monday was the first time GOP presidential candidate Mitt Romney and Florida Sen. Marco Rubio, often talked about as a vice presidential pick, have campaigned together. But Romney said the process of choosing his running mate has barely gotten started.

Voters are going to polls in Pennsylvania, Rhode Island, Connecticut, Delaware and New York, though turnout is expected to be low. Still, here are four things to watch. Even with Rick Santorum, out of the race, Pennsylvania could still be interesting if Ron Paul's supporters are able to spring a delegate surprise on Mitt Romney.

Mitt Romney will still be the presumptive nominee. But analysts say Newt Gingrich might win today in Delaware. That could give him a reason to stay in the race.

President Obama won 2 out of 3 Hispanic votes in 2008, and Democrats this election season have a growing advantage with Hispanics. But Republicans and likely nominee Mitt Romney say they have a strong case to make for those votes based on the economy, and some are trying to shift focus away from Romney's stance on immigration.

Calls for Rick Santorum to leave the Republican race only increased after he failed to win any of Tuesday's primaries. But if Santorum and his team were close to taking that advice, that didn't come across in an interview NPR's Audie Cornish, an All Things Considered co-host, conducted with John Brabender, a top adviser to the former U.S. senator from Pennsylvania.