As a reaction to the crack epidemic of the 1980s, many federal drug laws carry strict mandatory sentences. This has stirred unease in Congress and sparked a bipartisan effort to revise and relax some of the more draconian laws.

Traditionally — meaning before Barack Obama — that’s how laws were changed: We have a problem, we hold hearings, we find some new arrangement ratified by Congress and signed by the president.

That was then. On Monday, Attorney General Eric Holder, a liberal in a hurry, ordered all U.S. attorneys to simply stop charging nonviolent, non-gang-related drug defendants with crimes that, while fitting the offense, carry mandatory sentences. Find some lesser, non-triggering charge. How might you do that? Withhold evidence— for example, the amount of dope involved.

In other words, evade the law, by deceiving the court if necessary. “If the companies that I represent in federal criminal cases” did that, said former deputy attorney general George Terwilliger, “they could be charged with a felony.”

But such niceties must not stand in the way of an administration’s agenda. Indeed, the very next day, it was revealed that the administration had unilaterally waived Obamacare’s cap on a patient’s annual out-of-pocket expenses — a one-year exemption for selected health insurers that is nowhere permitted in the law. It was simply decreed by an obscure Labor Department regulation.

Which followed a presidentially directed 70-plus percent subsidy for the insurance premiums paid by congressmen and their personal staffs — under a law that denies subsidies for anyone that well-off.

Which came just a month after the administration’s equally lawless suspension of one of the cornerstones of Obamacare:the employer mandate.

Which followed hundreds of Obama­care waivers granted by Health and Human Services Secretary Kathleen Sebelius to selected businesses, unions and other well-lobbied, very special interests.

Nor is this kind of rule-by-decree restricted to health care. In 2012, the immigration service was ordered to cease proceedingsagainst young illegal immigrants brought here as children. Congress had refused to pass such a law (the DREAM Act) just 18 months earlier. Obama himself had repeatedly said that the Constitution forbade him from enacting it without Congress. But with the fast approach of an election that could hinge on the Hispanic vote, Obama did exactly that. Unilaterally.

The point is not what you think about the merits of the DREAM Act. Or of mandatory drug sentences. Or of subsidizing health care premiums for $175,000-a-year members of Congress. Or even whether you think governors should be allowed to weaken the work requirements for welfare recipients — an authority the administration granted last year in clear violation of section 407 of the landmark Clinton-Gingrich welfare reform of 1996.

The point is whether a president, charged with faithfully executing the laws that Congress enacts, may create, ignore, suspend and/or amend the law at will. Presidents are arguably permitted to refuse to enforce laws they consider unconstitutional (the basis for so many of George W. Bush’s so-called signing statements). But presidents are forbidden from doing so for reasons of mere policy — the reason for every Obama violation listed above.

Such gross executive usurpation disdains the Constitution. It mocks the separation of powers. And most consequentially, it introduces a fatal instability into law itself. If the law is not what is plainly written, but is whatever the president and his agents decide, what’s left of the law?

The problem is not just uncertain enforcement but the undermining of the very creation of new law. What’s the point of the whole legislative process — of crafting various provisions through give-and-take negotiation — if you cannot rely on the fixity of the final product, on the assurance that the provisions bargained for by both sides will be carried out?

Consider immigration reform, now in gestation. The essence of any deal would be legalization in return for strict border enforcement. If some such legislative compromise is struck, what confidence can anyone have in it — if the president can unilaterally alter whatever (enforcement) provisions he never liked in the first place?

Yet this president is not only untroubled by what he’s doing, but open and rather proud. As he tells cheering crowds on his never-ending campaign-style tours: I am going to do X — and I’m not going to wait for Congress.

That’s caudillo talk. That’s banana republic stuff. In this country, the president is required to win the consent of Congress first.

At stake is not some constitutional curlicue. At stake is whether the laws are the law. And whether presidents get to write their own.

Read more from Charles Krauthammer’s archive, follow him on Twitter or subscribe to his updates on Facebook.