The last time President Trump held office, he tried to make deep cuts to foreign aid, but was blocked by Congress. He is finding little resistance from fellow Republicans this time to his move to freeze such funding.

During a special counsel’s inquiry in his first term, Mr. Trump expressed a desire to fire the investigator, but White House lawyers stopped him. This term, Mr. Trump has swiftly forced out a slew of federal officials who had oversight roles over his administration.

In the final days of his first presidency, Mr. Trump tried to hire a loyalist to help run the F.B.I., until Attorney General Bill Barr objected, Mr. Barr said in his book after he left office. Now that same loyalist, Kash Patel, is poised to lead the bureau.

At every step in his second term, Mr. Trump is demonstrating how unbound he is from prior restraints, dramatically remaking both domestic and foreign policy at a scale that has little parallel. His swift moves in his first month back in office underscore the confidence of an administration with a much firmer grip on the levers of government than during Mr. Trump’s last stint in the White House.

Long gone are the veterans of the Bush and Reagan administrations who pushed him to hew to more traditional conservative policies. In their place are a group of mostly America First Republicans helping Mr. Trump radically reset the country’s policies — as well as the billionaire Elon Musk, whom the president has unleashed to barrel through the bureaucracy.

“We’ve never seen anything on the scale of what Donald Trump’s new administration is doing,” said Jeffrey A. Engel, who leads the Center for Presidential History at Southern Methodist University. “It’s not just a reversal of previous administration policies — which we always expect to see a little bit of — but a reversal of the fundamentals of American foreign policy since 1945.”