Exclusive: Obama Begins Historic Visit in Cuba: 'Change Is Going to Happen' The US president spoke to ABC's David Muir during his first visit to Havana.

 -- President Obama told ABC News anchor David Muir in an exclusive interview Sunday in Havana, Cuba, that "change is going to happen" in the island nation.

"The time is right. Obviously our intention has always been to get a ball rolling, knowing that change wasn't going to happen overnight. ... We felt that coming now would maximize our ability to prompt more change. ... And it gives us, I think, the opportunity before I leave office to continue to stay on track in moving things forward," Obama said as he began his two-and-a-half-day visit to the Cuban capital. "Change is going to happen [in Cuba] and I think that [President] Raul Castro understands that."

The trip marks the first time in nearly 90 years a sitting U.S. president has visited Cuba. Obama announced the trip via Twitter in February.

President Obama's exclusive sit-down interview with David Muir will air Monday on "World News Tonight with David Muir" at 6:30 p.m. ET and on "Nightline" at 12:35 a.m.

The president's trip comes 15 months after he announced the restoration of diplomatic ties between the U.S. and Cuba. In the last year, U.S. officials have worked to reopen Cuba to America with historic agreements, including direct flight agreements.

"We still have some work to do," Obama told Muir today. "I think it is very important for the United States not to view ourselves as the agents of change here, but rather to encourage and facilitate Cubans themselves to bring about changes. ... We want to make sure that whatever changes come about are empowering Cubans."

On Monday, Obama is scheduled to participate in an official state visit, including a bilateral meeting with Castro and a state dinner. The two men first met face-to-face during a summit in Panama last year.

He will also speak to entrepreneurs in the country. Obama is being joined by a massive U.S. delegation during his visit; 39 members of Congress including five Republicans will be following his movements.

The president also plans to address the Cuban people directly in a historic speech Tuesday and will take in an exhibition game between the Tampa Bay Rays and the Cuban National team.