Sen. John McCain takes his campaign to Mexico and Colombia this week, where he’ll tackle two key issues on many voters’ minds: free trade and immigration. McCain was due to start the three-day trip Tuesday in Colombia.

McCain has been a strong supporter of free-trade agreements and NAFTA, and he knows they are a tough sell in the current economic environment. They will be especially tough to sell in swing states — Ohio, Pennsylvania, Wisconsin, Michigan — that have been losing manufacturing jobs to cheaper labor across the borders.

“I have to convince them the consequences of protectionism and isolationism could be damaging to their future,” the McCain said Tuesday in Philadelphia, before departing for South America. “I understand it’s very tough. But for me to give up my advocacy of free trade would be a betrayal of trust. And the most precious commodity I have with the American people is that they trust me.”

In Cartagena, Colombia, McCain will meet with President Alvaro Uribe and several cabinet members. They are sure to discuss a proposed free-trade package that is supported by McCain but is hung up in Congress.

House members have blocked a vote on the package because of concerns over Colombia’s record on human rights and stopping drug trafficking, and reports of violence against labor rights groups. McCain, however, has said Colombia’s human rights issues should not stop passage of the agreement.

In Mexico, McCain will talk about immigration, and conservatives will be listening closely to what the senator says. McCain upset many conservatives when last year he co-sponsored, with Sen. Ted Kennedy, legislation to allow illegal immigrants to stay in the United States after paying fines and back taxes and going through a background check. Many conservatives called the legislation an “amnesty bill.” The legislation ultimately failed, but conservatives have not forgotten.

“I expect to be supporting him in November,” Rep. Tom Tancredo, the former anti-immigration presidential candidate, told Time Magazine last week in an interview about McCain. “But certainly it is not set in stone.”