In a speech that emphasized Romney's plans for the economy, Rubio also spoke of his own immigrant roots.
It's also no accident that Obama peppers some of his speeches with a bit of Spanish. Latinos are the fastest-growing subset of American voters, and that makes immigration, a crucial nexus of domestic and foreign affairs, a key issue in Tuesday's vote.
"Rubio represents somebody who can be seen as sympathetic to the immigrants' cause, but also recognizes that the rule of law is important," said Andrew Atkins, 27, a human-resources consultant who drove in from Valley Forge for the rally.
Polls show Latinos favoring Obama by as much as 3-1. Still, "If immigrants like Rubio," said Atkins' mother, Marsha, who also went to the rally, "he can pull some votes."
Though both the president and the former Massachusetts governor speak of a "broken" immigration system ripe for reform, they favor fundamentally different approaches to the hotly contested problem of illegal immigration.
Early in his GOP primary campaign, Romney offered hard-line solutions such as "self-deportation" for the nation's estimated 11 million illegal immigrants.
He since has softened his tone somewhat, but still supports tough, Arizona-style laws and opposes efforts to give legal status to unauthorized immigrants without first requiring that they leave the country. His top adviser on this issue heads the movement to give states more latitude in enforcement.
The president, for his part, has deported a record 1.5 million illegal immigrants since 2009 while initiating temporary relief from removal for immigrants who arrived as children and who meet certain criteria. He believes federal law preempts most independent state action on immigration.
What follows are the candidates' positions on some of the main points of contention in the immigration debate:
Securing the border. The fence along the U.S.-Mexico border has long been a political football.
Federal officials say the 650-mile barricade mandated under the Secure Fence Act of 2006 is virtually complete.
At the same time, Republicans say a 2007 amendment basically gutted the law by giving border patrol agents the power to decide which type of fence - anti-vehicle or anti-pedestrian - is appropriate in various terrain. The original law called for two parallel lines of anti-pedestrian fence throughout.
A 2011 report from the Government Accountability Office deemed the southwest border adequately fenced, or "under operational control," but said it "continues to be vulnerable" to human smuggling.
In June, Romney called for a "high-tech fence" of sensor towers. A year earlier, Obama said of GOP hard-liners, "maybe they'll need a moat. Maybe they want alligators in the moat. They'll never be satisfied. . . . That's politics."
The DREAM Act and DACA. Among the population of illegal immigrants are millions of young people who were brought here as children. Raised as Americans, they know no other home.
Obama supports the proposed Development, Relief, and Education for Alien Minors (DREAM) Act, which would put undocumented youths on a path to citizenship provided they entered the United States before turning 16, completed high school or earned a GED, have no criminal record, and lived here continuously for at least five years. If eligible, they would have six years in which to obtain a two-year college degree or complete two years of military service.
An attempt to pass the DREAM Act was defeated in the Senate in 2010.
In June, Obama used his executive authority to promulgate Deferred Action for Childhood Arrivals, known as DACA. To be eligible, petitioners must have been younger than 16 when they arrived, younger than 31 when the initiative was announced, have a high school diploma or GED, or have served honorably in the military. If they meet those criteria, they get a work permit and a renewable, two-year deferment from deportation.
Romney has said he opposes the DREAM Act; he and others who support strict immigration control say DACA is no better. At the same time, he said he wants to provide relief for DREAM Act-eligible youths under an as-yet unspecified plan for comprehensive immigration reform.
His campaign told the Boston Globe in October that Romney would not revoke work permits of DACA recipients approved by Jan. 20 - the date he will take office if elected. He would grant no new permits after that.
Guest workers. The Republican platform calls for "a legal and reliable source of foreign labor" through a new guest-worker program. Romney supports the platform.
Union leaders and other foes of such programs say they exploit a revolving underclass of low-wage, easily abused workers.
Under the administration's current H-2B visa program, employers can hire temporary foreign workers for seasonal jobs if American workers aren't available. Depending on the season, about 115,000 such workers are employed in construction, landscaping, seafood processing, and other industries. H-2A visas are used similarly for guest agricultural workers.
Foreign students. Both candidates say they recognize America's need to attract and retain the brightest talent, no matter where it originates.
"If you get an advanced degree here, we want you to stay," Romney told a Latino audience in June. "So I'd staple a green card to the diploma of someone who gets an advanced degree in America."
Obama, in his 2011 State of the Union address, told of the frustration of seeing foreign students "come here from abroad to study in our colleges and universities . . . but as soon as they obtain advanced degrees, we send them back home to compete against us. It makes no sense."
Contact Michael Matza at 215-854-2541 or firstname.lastname@example.org.