Some who know Mr. Bolton and his operating style predict titanic clashes.

Defense Secretary Jim Mattis, the retired general who has argued for keeping the Iran deal intact and warned that military confrontation with North Korea would result in “the worst kind of fighting in most people’s lifetimes,” told colleagues on Friday that he did not know if he could work with Mr. Bolton. The White House chief of staff, John F. Kelly, another retired four-star general, was also unenthusiastic about Mr. Bolton’s hiring…

But others who have worked for years with Mr. Bolton argue that Mr. Trump knows exactly what he is getting: leverage, not conflict.

“I think this notion everybody talks about, that the risks of war have gone up, is wrong,” said Stephen J. Hadley, who was Mr. Bush’s national security adviser and a major architect of the invasions of Afghanistan in 2001 and Iraq in 2003. “This is the peace-through-strength crowd who want to make clear to people that they’re tough and that no one should cross them. But the reason for that is to deter war.”