When President-elect Donald Trump takes office, he can immediately begin to unravel nearly all of the steps the Obama administration has taken to normalize ties with Cuba, just as he threatened to do in a tweet. But experts say Trump most likely will face tough resistance and challenges. "He could break diplomatic relations on his first day in office," said William LeoGrande, professor of government at American University and co-author of "Back Channel to Cuba: The Hidden History of Negotiations between Washington and Havana." It most likely would take longer, perhaps months, to roll back changes in trade with and travel to Cuba, because the Treasury and Commerce departments would have to rewrite complex regulations. Regulatory changes President Barack Obama used his presidential authority to make nearly all the changes regarding Cuba,"so from a technical point of view, President Trump could undo all of those things reasonably quickly," said LeoGrande. The president-elect could reverse regulations that allow U.S. businesses and corporations to operate in Cuba and Obama's decision to allow so-called people-to-people travel there. With a single tweet on Monday, Trump cast doubt on the future of Obama's historic policy shift toward Cuba, one that pushed aside a decades-old policy of isolation in favor of one that promotes engagement. "If Cuba is unwilling to make a better deal for the Cuban people, the Cuban-American people and the U.S. as a whole, I will terminate deal," Trump tweeted. "Our priorities are the release of political prisoners, return of fugitives from American law, and also political and religious freedoms for all Cubans living in oppression," said Jason Miller, communications director for Trump's transition team. The president-elect and many Republicans in Congress have argued that Washington gave Havana too many concessions without insisting that the communist government end its oppressive policies and human rights abuses. 'Slam the door' But negotiating with Cuba will not be easy, experts caution. "If Trump sends people to Cuba to renegotiate the arrangements that Obama had negotiated with Cuba, with the idea that the Cubans would have to give more in terms of human rights or democracy, they would slam the door in his face," said Brian Latell, adjunct professor at Florida International University's Jack D. Gordon Institute for Public Policy. Since Obama announced the new Cuba policy in August 2014, the U.S. and Cuba have restored diplomatic ties, reopened embassies, greatly relaxed trade and travel restrictions, and signed 12 agreements on a range of interests, including telecommunications, health, aviation, and hospitality and tourism. U.S. businesses and corporations have made investments in the communist nation and soon will begin operating there, including Marriott International and Starwood Hotels & Resorts. In August, JetBlue Airways became the first airline to fly from the U.S. to Cuba in more than 50 years. In the coming months, there will be up to 110 daily flights between the two countries, according to the White House. It's "not as easy as just a stroke of a pen, because there will be consequences in doing that," said Josh Earnest, White House press secretary. "There will be an economic impact in the United States and in Cuba for unraveling that policy." Trump spokesman Miller said the president-elect was "aware of the nuances and challenges" regarding Cuba. Congressional input While Trump has said he wants to negotiate a better deal, it is unclear how much he is willing to reverse Obama's measures. "President Trump would be less inclined to make a deal if he got a tremendous push back from Capitol Hill, especially in the House of Representatives," said Raymond Tanter, who served on the National Security Council under President Ronald Reagan and now heads the American Committee on Human Rights. "I would say that there's a strong likelihood that the legacy of Obama will be very difficult to overturn." "The politics of it are very complicated," said LeoGrande. "The legalities of it are pretty straight forward in terms of what the president has the legal authority to do."