America is living through a constitutional crisis — and it didn’t start when President Donald Trump announced his administration would stonewall all congressional subpoenas and try to thwart Congress’ oversight efforts.

The U.S. Constitution imposes on Congress a duty to conduct effective oversight as part of its legislative duties.

Trump’s refusal to acknowledge this vital congressional power — and his affirmative plan to undermine it — is at odds with our basic constitutional system. Congressional oversight is central to our system of separation of powers — the idea that our democracy rests on decentralized power, with each of the three branches constraining the authority of the others.

It remains to be seen how far Trump is willing to go to subvert oversight — though all signs are bad.

Our constitutional crisis extends far beyond the fight over congressional subpoenas or even the congressional oversight function, however. Trump is, on a continuing basis, assaulting America’s core constitutional values, obligations, protections and guarantees. For example:

— From Day One, Trump has governed in violation of the Constitution’s core anti-corruption provision. The Constitution prohibits the president from accepting things of value (“emoluments”) from foreign governments without express congressional approval. But Trump continues to own his business empire, which not only accepts payment from foreign governments for hotel rooms but has properties and interests around the world that receive foreign governmental subsidies, payments and benefits.

— The First Amendment prohibits discrimination on the basis of religion. One of Trump’s earliest acts was to issue the Muslim ban, prohibiting entry into the United States by people from predominantly Muslim nations. The courts struck down this executive order, as they did a second. The U.S. Supreme Court, wrongly, let stand a third.

— Trump illegally evoked “emergency powers” to fund construction of a U.S.-Mexico border wall that Congress specifically refused to authorize. Trump’s action eviscerated separation of powers principles and Article I’s delegation of all funding authority to the Congress.

— The Constitution specifies that the president must “take care that the laws be faithfully executed.” Trump has repeatedly refused to do so, including by refusing to implement health, safety and other regulations called for by federal statute.

These examples are only a partial sampling of Trump’s constitutional transgressions. He has attacked the free press, labeling the media as the “enemy of the people,” a phrase used through history by dictators and authoritarians. He has attacked the independence of the judiciary, even as he as undermined judicial integrity by appointing a raft of extremist judges.

Although trite to say, the Constitution is really a remarkable document. Perhaps its most exceptional component is the Preamble. It is “we the people of the United States” who establish the Constitution.

We do so to “form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity.”

In short, we do so not just to order and arrange our government but to advance justice, protect liberty and take care of each other. Ultimately, our constitutional crisis tracks to Trump’s subversion of these principles and aspirations.

Trump is using the government to advance his own interests and those of connected corporations; he is fomenting hate against immigrants and people of color; and he stands ready to violate the law, rules, standards, norms and traditions to carry forward his parochial interests and defend his corrupt regime.

A crisis indeed.

Robert Weissman is the president of Public Citizen, a nonprofit consumer advocacy organization. This op-ed was distributed by InsideSources.com.