When he took office last week, President Trump said he would measure his success in part by “the wars we never get into.” But he has eagerly waged a full-fledged assault on his own government.

In his first eight days in office, Mr. Trump mounted a lightning blitz against the federal government that has the nation’s capital in an uproar. He has moved quickly and aggressively to eliminate pockets of resistance in what he calls “the deep state” and put his own stamp on far-flung corners of the bureaucracy.

It has been a campaign of breathtaking scope and relentless velocity, one unlike any new president has tried in modern times. It has been a blend of personal and political as he seeks revenge against those who investigated him or his allies, while simultaneously demolishing the foundations of the modern liberal state and asserting more control than he or any of his predecessors had in the past.

Mr. Trump has purged perceived enemies from a range of agencies; begun to rid the government of diversity, environmental, gender and other “woke” policies that he objects to; sought to punish those who acted against his interests in the past; and fired independent inspectors general charged with guarding against potential corruption and abuse by his administration. His directive to temporarily freeze trillions of dollars of federal spending touched off a firestorm and prompted a judge to block him, for now.

Mr. Trump presents this effort as a fundamental reorientation of government and politics, in effect reversing generations of change to return to a different bygone era. “We’re forging a new political majority that’s shattering and replacing Franklin Roosevelt’s New Deal coalition, which dominated American politics for over 100 years,” he told House Republicans at their retreat this week.

Never mind his faulty math — Roosevelt was first elected 92 years ago — Mr. Trump has approached his mission more systematically and methodically than he ever did in his chaotic first term, when he became the first U.S. president who had never served in public office or the military.

Instead of fumbling around to figure out how to even draft an executive order — his travel ban on select Muslim-majority countries eight years ago had changes scribbled on it by hand just minutes before he signed it — this time he and his team came in ready to quickly move forward on myriad fronts.

This was an odd benefit of losing his bid for re-election in 2020. As the first president since Grover Cleveland to come back to office after being defeated, Mr. Trump had the advantage of both four years of experience in the White House and four years in hiatus to map out plans for his return. Aided by a cadre of like-minded ideological advisers, he crafted a sweeping set of plans to quickly seize the reins of government.

The shock-and-awe onslaught has not just changed the government’s approach to major policies, as happens anytime a president of one party takes over from that of another. Mr. Trump is intent on “deconstruction of the administrative state,” as his onetime chief strategist Stephen K. Bannon put it during his first term, a goal predicated on the assumption that the bureaucracy is inherently biased against conservatives and their priorities.

“Trump is on a wrecking cruise to de-professionalize the civil service and threaten basic services to Americans,” said Representative Gerald E. Connolly, Democrat of Virginia, whose district includes many federal workers. “It’s unlawful firings and impoundments that threaten to unravel 142 years” of tradition of a “civil service immune from partisan politics.”

At the president’s order, the career prosecutors who worked for the special counsel Jack Smith on investigations into Mr. Trump have been fired. And after the president granted clemency to those who ransacked the Capitol on Jan. 6, 2021, an investigation was opened into the actions of career prosecutors who charged those Trump supporters.

Dozens of career officials at the National Security Council were sent home while their loyalty is being reviewed. Dozens of other career officials, at the U.S. Agency for International Development, were put on leave for suspicion of resisting an order by Mr. Trump. The Justice Department ordered a temporary halt to all civil rights enforcement.

Mr. Trump has also rescinded certain additional protections for senior civil servants enacted by former President Joseph R. Biden Jr., and this week he ordered a review of people in policy-making positions to ensure that they follow his administration’s priorities or face dismissal. The administration also offered an incentive to federal workers to resign as of Sept. 30 in hopes of encouraging a broad exodus so that slots can be filled with loyalists.

But the most explosive move so far was Mr. Trump’s order on Monday night temporarily freezing up to $3 trillion federal grants and loans to determine whether they meet his priorities, even though they had been passed by Congress. More than any other move, this order generated widespread Democratic protests and could have affected everyday Americans, including Mr. Trump’s own voters.

A federal judge in Washington on Tuesday stepped in to temporarily prevent it from taking effect, pending further review of its legality, capping a day of confusion. For all its efficiency so far, the Trump team stumbled over enactment of this order, unable to promptly answer basic questions about who it would affect and for how long.

At her debut briefing on Tuesday, Karoline Leavitt, the White House press secretary, assured Americans that it would not affect Social Security, Medicare, welfare or food stamps, but did not know whether it would affect Medicaid, which covers health care for 72 million Americans, most of whom are lower-income.

“The American people gave President Trump an overwhelming mandate on Nov. 5,” Ms. Leavitt said, referring to Mr. Trump’s 1.5-percentage-point popular vote victory, one of the smallest since the 19th century. “And he’s trying to ensure that the tax money going out the door in this very bankrupt city actually aligns with the will and priorities of the American people.”

A memo sent to Congress by the Office of Management and Budget on Tuesday insisted that Medicaid would not be affected by the order. But later in the day, the White House acknowledged that the online Medicaid portal was down even as it insisted that payments were still being processed and sent.

For all their loud criticism, congressional Democrats have limited ability to do much other than complain since they control neither house of Congress. Instead, Mr. Trump’s opponents are left to turn to the courts to try to stop him, as they did with the temporary spending freeze. Mr. Trump’s order on civil servants has already generated a legal challenge, and there could be more over his decisions to eliminate diversity programs and fire inspectors general.

Mr. Trump and his team anticipated pushback and expected to have to fight all the way to the Supreme Court to make some of these changes, hopeful that they will be ratified by the six-to-three conservative majority among the justices.

At one point while running for president again, Mr. Trump said he hoped to trigger a legal fight to overturn the Impoundment Control Act of 1974, which was passed after President Richard M. Nixon refused to spend billions of dollars appropriated by Congress.

The act enshrined into law a previous understanding that a president cannot unilaterally decide not to spend money that Congress had approved. The law laid out a process allowing spending items to be temporarily suspended during a fast-track request to lawmakers to rescind them.

“When I return to the White House, I will do everything I can to challenge the Impoundment Control Act in court, and if necessary, get Congress to overturn it,” Mr. Trump said in 2023. “We will overturn it.”

Whether he will succeed in overturning it or not, it may take a while to find out. But part of the point is to have the fight, win or lose. Even if he gets resistance on one front or another, Mr. Trump is sending a signal to the federal government: He plans to reshape it in his image and anyone who disagrees should get out of the way or he will try to run them over.