LONDON — He incensed Paris and London by saying that some of their neighborhoods were so overrun with radicals that the police were too scared to enter.

He raised Scottish tempers by threatening to pull the plug on his investments there, including his luxury golf courses, if British politicians barred him from entering Britain.

Now Donald J. Trump has upset the already beleaguered people of Belgium, calling its capital, Brussels, “a hellhole.”

Asked by the Fox Business Network anchor Maria Bartiromo about the feasibility of his proposal to bar foreign Muslims from entering the United States, Mr. Trump argued that Belgium and France had been blighted by the failure of Muslims in these countries to integrate.