US Cuba relations simply comes down to a small segment of US society called Cuban-Americans in Florida. Florida is a massive swing state providing a huge amount of electoral votes. As it currently stands, Republicans need a majority in Florida to have a chance at winning the Presidency. Cuban-Americans are the most opposed to normalizing relations. This is why Trump and Republicans push against normalizing relations, so they can get the Cuban-American block and win Florida. Democrats have to walk a fine line. Even when normalizing relations is the right thing, doing the opposite is what wins you the US presidential election.