The president-elect's undiplomatic talk in recent days of reclaiming the Panama Canal — and annexing Greenland and even Canada — have some experts comparing his strategy to Nixon's "Madman Theory."

President-elect Donald J. Trump refused on Tuesday to rule out the use of military or economic coercion to force Panama to give up control of the canal that America built more than a century ago and to push Denmark to sell Greenland to the United States.