WASHINGTON (Reuters) - It will be difficult for future U.S. administrations to undo President Barack Obama’s policy of easing trade and travel restrictions with Cuba because of the benefits associated with the measures, a senior U.S. official said on Friday. “We’ve increased the space for this type of travel, people to people exchange, commercial opportunities in ways that are already having a positive impact on the lives of Americans and Cubans,” the official said. “Turning back the clock on that policy would only take away those opportunities.”  