But in the case of Mr. Trump, there is a sense that the rush for change has superseded a study of unintended consequences.

The ban on immigration and visitors from seven nations came with minimal, if any, input from the State Department about the regional fallout — as did Mr. Trump’s declaration that he intends to move the American Embassy in Israel to Jerusalem. The absence of advance thinking about how to deal with green card holders and Iraqi interpreters who were promised entry to the United States in return for their service to American troops forced the White House to amend its interpretations of the order less than 48 hours after Mr. Trump signed it.

It was all symptomatic of a new president eager to tweet first and work out details later. “This is policy by thunderbolt,” said Joseph Nye, a Harvard professor who served as the head of the National Intelligence Council and has written extensively on how the United States can gain leverage from its “soft power” — the attractiveness of its culture and democracy. “You don’t want to tear up 70 years of foreign policy until you think hard about what replaces it.”

But inside the halls of the State Department, where Rex W. Tillerson, the pick for secretary of state, has just begun to find his way around, there is definitely the sense among career diplomats that this is Year Zero.

Last week, the “landing team” of Trump designees told several of the department’s most senior diplomats — career officials, some with decades of service — to clear out of their offices. Almost all had submitted their resignations, the protocol when administrations changed, but had volunteered to stay on for a month or two until successors were appointed, to ensure that State Department facilities were safe, American citizens were evacuated from perilous places and passports were issued.

The Trump team made it clear it had no interest in transitions. (Mr. Tillerson also never met one-on-one with his predecessor, John Kerry, before the inauguration.)

It was not exactly a purge, but the fact remains that some of the government’s most experienced diplomats have moved on — including some of the highest-ranking women in the department. Among them is Anne Patterson, 67, the assistant secretary of state for Near Eastern affairs and a former ambassador to Pakistan and Egypt, two of the biggest tinderboxes Mr. Trump will face. Victoria J. Nuland, 55, one of the department’s top Russia experts and former ambassador to NATO, who dealt with the Ukraine crisis, decided to retire after concluding there was probably no place for her in Mr. Trump’s administration.