Trump envisions Kelly executing his orders with military precision and steely gravitas, and without tending to outside political motivations or fretting about palace intrigue, according to Trump confidants. The president replaced Reince Priebus with Kelly, who had what Trump considers a star run as homeland security secretary, in the hope of projecting overall toughness and of inspiring the respect — and even fear — that has eluded him on Capitol Hill, where fellow Republicans last week defied the White House on health care and Russian sanctions.

But no matter how decisive his leadership, Kelly alone cannot turn Trump’s vision into reality. Warring internal factions that have stirred chaos, stoked suspicions and freelanced policies for six straight months may not easily submit to Kelly’s rule. And the president — whose rash impulses routinely have sabotaged the best efforts of his senior aides — has shown no willingness to be tamed.

“Kelly is an incredibly disciplined person who could bring order to the process if the animals in the zoo behave,” said John E. McLaughlin, a former acting director of the CIA who served in seven administrations. “The danger he has is that Trump will be Trump.”