Rick Santorum ended his bid for the Republican presidential nomination yesterday, making Mitt Romney the all-but-certain nominee. Newt Gingrich and Ron Paul are staying in the race, but now attention is shifting to Romney’s future choice of a running mate and uphill battle to replace President Obama.

Speculation that Santorum would quit the race rose after his three-year-old daughter, Bella, had to go to the hospital over the weekend. She suffers from Trisomy-18, a rare disorder that is fatal for all but one percent of its victims by age 10. She has been released from the hospital, but the decision to exit the race was still made.

Santorum described his campaign as being “about who we are as Americans” and reflected on how his campaign sprung from last place to runner-up, despite being counted out all the way up until the final weeks before the Iowa caucus. He is proud that his campaign didn’t focus solely on the economy, but also “violent radical Islam” and “the scourge of Iran.”

There were other factors in his decision. His campaign is asking supporters to help pay off debt, saying the campaign “can’t be free to focus on helping defeat [Obama] with this burden.” Romney had also attained a nearly insurmountable delegate lead. His rivals were under tremendous pressure to drop out due to fears that a prolonged campaign would give Obama decisive advantages. He was also declining in the polls in his home state of Pennsylvania. A game-ending Romney victory there on April 24 was becoming more likely.

Newt Gingrich and Ron Paul are committed to staying in the race. Gingrich immediately declared himself the “last conservative standing”  and says he is eager to go one-on-one with Romney. He hopes to debate him in North Carolina before the state holds its primary on May 8. It is highly unlikely Romney will agree.

Gingrich is focusing on winning delegates in Delaware on April 24, North Carolina on May 8 and Texas on May 29. He admits that Romney is “far and away” the most likely one to get the nomination, so he instead is focusing on influencing the party platform. According to the Republican National Committee, Romney currently has 573 delegates. Even if all of Santorum’s delegates jumped to Gingrich, he’d only have 334.

The Obama 2012 campaign starts off with a huge financial and organizational advantage. It has about $84.7 million and 530 paid staff members, whereas Romney has only $7.3 million and about 100 paid staff members. Josh Kraushaar argues that super-PACs aligned with Romney make up this difference.

At the moment, the polls favor Obama. He is ahead of Romney by an average of 5.3%, according to RealClearPolitics. He has grown his lead among independents in the swing states by 4% since February, 48 to 39. Political analyst Dick Morris says the polls are deceitful because about 80% of the undecided vote goes against the incumbent at the last moment.

Obama has comfortable leads in Ohio (8.6%), Nevada (6.7%) and Pennsylvania (6%). His leads are much smaller in North Carolina (3%), Iowa (3%), New Hampshire (3.5%), Florida (3.5%) and Virginia (4%). As of right now, Obama would win 347 electoral votes to Romney’s 191. Of course, the general election campaign hasn’t even begun yet and these numbers will greatly fluctuate.

Romney has had leads over Obama in several of these states before. This is important because it indicates the voters are open to choosing him. Romney is ahead in Virginia by 5% in the latest poll. He led Obama in New Hampshire throughout last year, often by double-digits. There have been polls showing Romney with small leads in Iowa, Florida and Pennsylvania.

The general election campaign now begins in earnest. If you thought that the Republican primary was nasty, you haven’t seen anything yet.

According to 270toWin.com, the Democrats can count on 196 electoral votes and the Republicans can count on 181 electoral votes. The election will be decided in 13 battleground states. The poll averages in these states strongly favor Obama at the present time. Of these, Romney only leads in Missouri (9%). Obama has double-digit leads over Romney in New Mexico (16% in the last poll), Colorado (13% in the last poll), Wisconsin (11.8%) and Michigan (11.3%).

The focus will now be on Romney’s running mate and the general election. The most mentioned names are Florida Senator Marco Rubio, New Jersey Governor Chris Christie, Ohio Senator Rob Portman, Wisconsin Representative Paul Ryan and Virginia Governor Bob McDonnell. Sarah Palin and Herman Cain suggest Florida Representative Allen West.

Ryan Mauro is a fellow with RadicalIslam.org, the founder of WorldThreats.com and a frequent national security analyst for Fox News Channel. He can be contacted at ryanmauro1986@gmail.com.