FIFA, global soccer’s governing body, declined to comment on the Twitter post. A FIFA spokesman, however, did point to its pre-existing rules of conduct, which warn governments of bidding nations not to participate in activities that “may adversely affect the integrity of the bidding process and create an undue influence on the bidding process.”

The host of the 2026 World Cup will be named June 13, a day before the opening match of the 2018 World Cup in Russia. Even before Mr. Trump’s remarks, the North American bid was not considered a lock against its only rival, the North African nation of Morocco, even though the United States has an abundance of large stadiums and, in 1994, sold more tickets than any World Cup before or since.

Geopolitics always come into play when selecting hosts for the largest international sporting events, the World Cup and the Olympics. And Mr. Trump is unpopular internationally, in part because of his travel ban on residents from several predominantly Muslim nations and because of his reported vulgar remarks about accepting immigrants from developing countries, including those in Africa.