WASHINGTON (AP): John McCain was discussing the thorny issue of immigration Thursday with Mexican President Felipe Calderon, as the Republican presidential candidate wrapped up a three-day visit to Colombia and Mexico designed to promote free trade and burnish his foreign policy credentials.

McCain, whose home state of Arizona borders Mexico, was also visiting the Basilica de Guadalupe, Mexico's holiest site for Catholics. Hispanics and Catholics are expected to be key swing voters in the November election against Democrat Barack Obama, who has also worked to woo the same groups.

The Republican was meeting with Calderon to discuss illegal immigration, a key issue for Hispanic voters but a sore subject for many conservative voters who oppose efforts to allow some of the roughly 11 million such immigrants to eventually gain U.S. citizenship. McCain backs increased security along the U.S.-Mexico border to block the flow of undocumented workers.

Both Obama and McCain have been reaching to the center to appeal to undecided moderate voters, who are more likely to be Hispanic, Catholic and married with children than other voters. A recent AP-Yahoo News poll finds that 15 percent call themselves moderates and are not solidly supporting a candidate.