Former Pennsylvania Sen. Rick Santorum, left, speaks as former Massachusetts Gov. Mitt Romney listens at the South Carolina Republican presidential candidate debate in Myrtle Beach, S.C., Monday, Jan. 16, 2012. (Credit: Pool,AP Photo/Charles Dharapak)
Washington (CNN) -- As likely Republican presidential nominee Mitt Romney aims his firepower at President Barack Obama, he still has to protect his flank from rival Rick Santorum in a primary battle that Romney has all but won.
The former Massachusetts governor painted that picture while campaigning Thursday in Pennsylvania ahead of the state's April 24 primary.
Asked if Santorum, the ex-senator from Pennsylvania, would win in his home state, Romney said, "I think everybody expects someone to win their home state. Newt Gingrich won his state. I won my state. I think people expect the senator to win his home state. But I hope to pick up a lot of delegates, and we have several other states in the contest on the same day. I would like to win all of those, and if I can win the others and pick up some delegates here, it would give me a stronger lead."
But at the same time Romney quickly pivoted to the general election, adding that "I think I will win Pennsylvania in the fall. And a win in Pennsylvania will give us the White House."
It's a delicate dance that Romney must perform. Thanks to his string of primary victories, his extremely large lead in delegates and a slew of big-name GOP endorsements recently, Romney is considered by many to be the inevitable nominee.
While he's more than halfway there, Romney still has got a long way to go to win the 1,144 delegates needed to clinch the nomination. And as of now Santorum doesn't sound like he's ready to give up his bid for the White House.
"We have to win here and we plan on winning here," Santorum said Thursday while campaigning in Pennsylvania. "Then we're going to get into May. May looks very, very good."
Santorum's outlook is accurate. Most of the states holding primaries in May are more conservative than those in April and could provide Santorum with some victories if he lasts that long.
But at this point, it's not about winning contests -- it's about winning the nomination, and Romney has a nearly insurmountable lead.
Four years ago, in a much closer race, Hillary Clinton won five of the last eight primaries against Obama, but in the end, Obama captured the Democratic presidential nomination.
Pennsylvania is one of five states holding primaries April 24. The other four -- New York, Connecticut, Delaware and Rhode Island -- most likely favor Romney. And even in Pennsylvania, Santorum's once double-digit lead has disappeared, according to the most recent surveys, which indicate the candidate now holds only a single-digit advantage over Romney.
One question facing the Romney campaign is how much money it should invest in TV ads in Pennsylvania. Its ad spending advantage over Santorum in previous primaries has helped the former Massachusetts governor capture some crucial contests. But can the campaign now afford to put its resources almost entirely toward the general election?
Pennsylvania hasn't voted Republican in a presidential election since 1988, but the GOP would love to put the state in play this autumn. Positive primary commercials about Romney could help boost him in the state come November.
On the campaign trail, Romney has increasingly turned his attention toward the president.
Romney fired back the following day after Obama mentioned him by name in a speech Tuesday before the Newspaper Association of America, linking his likely fall opponent to a congressional Republican budget that the president slammed.
"While I understand the president doesn't want to run on his record, he can't run from his record either," Romney said in an address to the same group, adding that "this is not the time for President Obama's hide-and-seek campaign."
Romney tried to start his general-election campaign earlier but had to fend off surges, first by Gingrich, then Santorum. He might now be able to stay focused on Obama, one Republican strategist said.
"If you go back several primary nights ago, you can see Gov. Romney trying to train his fire away from Rick Santorum or Newt Gingrich or others and on to the president. This time it appears it may stick," said Gentry Collins, a former political director for the Republican National Committee and the Republican Governors Association.
"And it will stick not only because he's won the past several contests and has a commanding delegate lead but also because conservative and establishment Republicans now are coming out and endorsing him."
While the candidate steps up his attacks, his campaign is stepping up its efforts to transform from a primary outfit to a general-election operation. General-election fundraising is getting under way.
On Thursday, the Boston-based Romney campaign announced that a top GOP strategist, former Republican National Committee Chairman Ed Gillespie, will join its team as a senior adviser.
"Boston has been known in the past as an insular organization full of very capable people. But they didn't reach out to a lot of the folks over the past several years. They have now really changed their posture," said Collins, who ran Romney's 2008 operation in Iowa but who remains neutral this cycle.
"Gillespie is the most prominent to be announced, but the campaign has been aggressively reaching out to Republican strategists and operatives at a tactical level around the country, so I think you'll see pretty aggressive growth here in the next couple of months."