Donald Trump in a second term would likely install loyalists in key positions in the Pentagon, State Department and CIA whose primary allegiance would be to him, allowing him more freedom than in his first presidency to enact isolationist policies and whims, nearly 20 current and former aides and diplomats said.

The result would enable Trump to make sweeping changes to the U.S. stance on issues ranging from the Ukraine war to trade with China, as well as to the federal institutions that implement – and sometimes constrain – foreign policy, the aides and diplomats said.

During his 2017-2021 term, Trump struggled to impose his sometimes impulsive and erratic vision on the U.S. national security establishment.

He often voiced frustration at top officials who slow-walked, shelved, or talked him out of some of his schemes. Former Defense Secretary Mark Esper said in his memoir that he twice raised objections to Trump’s suggestion of missile strikes on drug cartels in Mexico, the U.S.’s biggest trade partner. The former president has not commented.

“President Trump came to realize that personnel is policy,” said Robert O’Brien, Trump’s fourth and final national security adviser. “At the outset of his administration, there were a lot of people that were interested in implementing their own policies, not the president’s policies.”

Having more loyalists in place would allow Trump to advance his foreign policy priorities faster and more efficiently than he was able to when previously in office, the current and former aides said.