President Barack Obama arrived to small but cheering crowds on Sunday at the start of a historic visit to Cuba that opened a new chapter in U.S. engagement with the island`s Communist government after decades of hostility between the former Cold War foes.The three-day trip, the first by a U.S. president to Cuba in 88 years, is the culmination of a diplomatic opening announced by Obama and Cuban President Raul Castro in December 2014, ending an estrangement that began when the Cuban revolution ousted a pro-American government in 1959."It`s a historic opportunity to engage directly with the Cuban people," Obama told staff at the newly reopened U.S. Embassy who were gathered at a hotel, his first stop after arriving in the afternoon.Groups of Cubans watched the motorcade from balconies and backyards as Obama was driven downtown, where a small crowd of Cubans braved a tropical downpour and tight security. They chanted: "Viva Obama, Viva Fidel," as the president and his family left after eating dinner in a rundown neighborhood. Obama, who abandoned a longtime U.S. policy of trying to isolate Cuba, wants to make his policy shift irreversible even if a Republican wins the White House in the Nov. 8 election.But major obstacles remain to full normalization of ties, and the Democratic president`s critics say the visit is premature. U.S. officials concede the trip may not yield immediate concessions from Cuba on rights and economic freedom.On Sunday, one bystander shouted: "Down with the blockade," in reference to the U.S. embargo in place for 54 years that remains the top irritant for Cubans. Obama, who responded to the shout by raising his right hand, has asked Congress to rescind the embargo but has been blocked by the Republican leadership.Underscoring the ideological divide that persists between Washington and Havana, Cuban police, backed by hundreds of pro-government demonstrators, broke up the regular march of a leading dissident group, the Ladies in White, detaining about 50 people just hours before Obama arrived.