Nearly every president has pushed the bounds of executive power to try to achieve something specific. And a handful of presidents who took office during a true national crisis, like the Civil War or the depths of the Great Depression, swiftly made a series of legally aggressive moves to grapple with the challenges facing the country.

But the sheer volume and intensity of the power grab President Trump has undertaken in the first 100 days of his second term — an assault on legal constraints untethered to any equivalent catastrophe — is unlike anything the United States has experienced.

“They are trying to do a moonshot on executive power,” said Jack Goldsmith, a Harvard Law School professor and senior Justice Department official in the George W. Bush administration.

The rule of law in the United States has been traditionally understood to use checks and balances to prevent too much concentration of arbitrary executive power. But the maximalist cascade in the early days of Mr. Trump’s second term is testing the fundamental structures of American democracy in a way that has never been seen before.

Mr. Trump, pursuing a confrontational style of presidential politics, has unleashed an assault on counterweights to his authority: attacking judges, sidelining Congress’s role in making decisions about taxes and spending, steamrolling internal limits on the executive branch and using the levers of government to try to force outside centers of power like law firms and universities to submit to his will.

Akhil Reed Amar, a Yale Law School professor, said the broader picture was of an administration that was “proudly lawless and anti-law.” The danger, he added, “is that Trump is the most powerful person in the world, and he does not seem to be very good at restraining himself and he’s not getting any younger.”