The next U.S. president will have to come to terms with leftist changes that have swept through Latin America and will face tough choices on issues including trade and drugs.
Leftists have been voted into power by targeting discredited economic and political reforms of earlier decades. Ecuador has booted the U.S. military from its last remaining base in the region. Venezuela is stocking up on Russian arms, and both Bolivia and Venezuela recently expelled U.S. ambassadors.
Adding to potential U.S. woes, China and Russia flaunt new economic and military deals in the region, while violent drug gangs from Mexico and Central America continue to expand.
If this were not enough, the new American president will have to deal with immigration, Cuba's likely transformation from the Castro era, and free-trade deals amid a global economic downturn.
Mr. McCain stresses strengthening democratic states, expanding trade and rebuilding the U.S.-Mexico partnership.
Mr. Obama, who has never been to Latin America but whose campaign has put forward a 13-page policy statement on the region, agrees with some of Mr. McCain's policies but diverges significantly on others.
For example, Mr. Obama has said that he would give Cuban-Americans unrestricted rights to visit their families and send remittances to the island nation. But like Mr. McCain, he would keep the half-century-old trade embargo and hold back on foreign aid, unless the regime undertakes democratic reforms, beginning with freeing political prisoners.
"From Cuba to an increase in development assistance to the call for a hemispherewide energy partnership, Barack Obama will change the status quo," said Wendy Morigi, a spokeswoman for the campaign. "John McCain has not spelled out how he would change the Bush policies that have created a vacuum in the Americas into which [Venezuelan President Hugo] Chavez, China and even Russia have stepped."
Mr. McCain has said he would push Cuba to release prisoners, legalize political parties and labor unions, free media outlets and hold internationally monitored elections. He also has criticized Mr. Obama's willingness to sit down with Cuban leaders before such changes take place.
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Mr. McCain also has chided Mr. Obama for suggesting that he would consider meeting Mr. Chavez, whose country provides 10 percent of U.S. oil imports.
"Barack Obama has said he would meet with the dictators of Venezuela and Cuba unconditionally in his first year in office," said Randy Scheunemann, Mr. McCain's chief foreign policy adviser. "John McCain would not bow down before dictators like Chavez or the Castro brothers."
On drugs and crime, both candidates support the Merida agreement, a $400 million program that seeks to bolster the Mexican government's war on drug cartels. Mr. Obama has said he wants to augment the program with a strategy that addresses the U.S. demand for drugs and also stems southward gun flows.
Both candidates support giving the Colombian military money to fight coca growers and back pre-emptive strikes against insurgent guerrilla bases in neighboring states.
Mr. McCain is also eager to give Colombia a free-trade deal, something Bogota wants badly.
Michael Shifter - vice president for policy of the Inter-American Dialogue, a Washington-based group that favors closer hemispheric ties - said Latin Americans in general prefer Mr. Obama's approach.
"Obama's tone, style, cosmopolitanism and racial mix appeal to many in the region," Mr. Shifter said. "They also like his emphasis on diplomacy and multilateralism, in contrast to what they see as McCain's more Cold War mind-set, viewing the region as divided between America's friends and adversaries."
Most Latin Americans also "desperately want an American president who can fix the current financial mess and get its own house in order, since Latin America is being profoundly affected by the downturn in the U.S. and globally," Mr. Shifter said. "Obama appears steadier and more reassuring on that score."
However, on some specific issues, such as trade, Latin governments prefer Mr. McCain, Mr. Shifter said. "The Brazilians in particular like McCain's view on removing ethanol subsidies and would hope that Obama would at least reconsider his position."
Mr. McCain sees free trade as key to lifting the region from poverty.
He supports the North American Free Trade Agreement (NAFTA), free-trade deals with Panama and Peru as well as Colombia, and seeks to revive the Free Trade Area of the Americas - a hemispheric concept opposed by many Latin American nations.
Mr. Obama opposed the Central American Free Trade Agreement (CAFTA) and wants to amend NAFTA. He also thinks free markets need regulatory intervention and wants changes in the economic and political conditions linked to loans given poor countries by Washington-backed institutions such as the International Monetary Fund.
Mr. Obama also would cancel the multilateral debts of poor, highly indebted nations such as Haiti, Bolivia and Honduras, said Miss Morigi, the Obama spokeswoman.
Mr. Scheunemann of the McCain campaign said Mr. Obama's opposition to free trade with Colombia and desire to renegotiate NAFTA reflect "pandering to big labor bosses." Such policies "would harm relations with our two largest trading partners at a time when we need the jobs dependent on exports more than ever before," Mr. Scheunemann said.
For both candidates, Latin America is a major factor in dealing with climate change and energy policy. Besides lifting import duties on sugar-cane-based ethanol from Brazil, Mr. McCain would implement a cap-and-trade plan to lower U.S. greenhouse gas emissions.
Mr. Obama would let U.S. emitters of greenhouse gases offset some of their emissions by investing in low-carbon energy projects in the developing world. His campaign literature also says that he would look for "incentives to maintain Latin American forests" in sustainable ways.
On immigration, Mr. Obama calls for simultaneously tightening border security and providing an easier path to U.S. citizenship for immigrants from the south. Mr. McCain stresses border security first.
Latin Americans preferred the more liberal position on immigration reform that Mr. McCain initially expressed but have become concerned about his more hard-line stance in the campaign, Mr. Shifter said.
If Latin Americans had their way, he added, both U.S. candidates also would "think more seriously about what they consider to be a failed drug policy, beyond backing assistance for the Colombian and Mexican governments."