President Barack Obama’s visit to Cuba is another step in the administration’s policy to normalize relations between the United States and the island nation which has been the object of a trade embargo for more than 50 years.

In December 2014, Obama announced that the U.S. and Cuba would restore diplomatic relations. Since then, Obama has relaxed restrictions on commerce and travel, and the State Department removed Cuba from its list of state sponsors of terrorism, and the two countries have reopened embassies in each other’s capitals.

The U.S. economic embargo, a major obstacle to improving ties with Cuba and the rest of Latin America, can be repealed only by Congress, a move many Republicans majority oppose. Obama and Democratic presidential candidates have called on Congress to lift the long-standing embargo. The remaining Republican presidential candidates have varying positions on the issue.

Former Secretary of State Hillary Clinton embraces the normalization of ties with Cuba. In July 2015 she called for lifting the economic embargo. As president, Clinton said she would use executive authority to further reduce trade and travel restrictions if Congress doesn’t lift the embargo. In her book, Hard Choices, Clinton wrote that as secretary of state she urged President Obama to reconsider the embargo.

Clinton formerly exhibited a more hardline stance toward Cuba. As first lady, she supported the 1996 Helms-Burton Act, signed into law by her husband, which strengthened the U.S. embargo against Cuba. During the 2008 presidential campaign, Clinton opposed lifting the embargo.

Senator Bernie Sanders supports the normalization of U.S.-Cuba ties and lifting the trade embargo. “My hope is that Cuba moves toward a more democratic society while, at the same time, the United States will respect the independence of the Cuban people,” Sanders said in February 2014.

Sanders participated in a congressional delegation to Cuba in February 2014. Last year he cosponsored a bill that would allow travel between the United States and Cuba.

Donald Trump supports diplomacy with Cuba. “Opening with Cuba is fine,” he said in September 2015,  but he criticized Obama for not making a better deal. In 1999, the real-estate developer wrote in favor of the embargo.

Senator Ted Cruz, whose father was born in Cuba, opposes Obama’s Cuba policy, calling it a “tragic mistake.” In December 2014, Cruz wrote that “the United States should demand that the political opposition to the Castros be included in any and all negotiations with Cuba, so their concerns will be fully heard and their priorities addressed.” Cruz believes the of the economic embargo should eased in proportion to the cessation of human rights violations In Cuba.

Governor John Kasich, as a member of the U.S. House of Representatives, voted against measures which would have eased economic and travel restrictions with respect to Cuba. He has not yet spoken on the issue as a presidential candidate.

Peter Buxbaum is web editor of Global Trade.