This is an adapted excerpt from MSNBC legal correspondent Lisa Rubin’s YouTube series “Can They Do That? With Lisa Rubin.”

During Donald Trump’s first few weeks in office, the president has issued a flurry of executive orders aimed not just at reshaping the federal government, but at removing all checks on his own power. Dozens of lawsuits have been filed against these actions, with many arguing the Constitution does not grant the president the authority he now seeks to assert.

The first and most important thing to keep in mind when considering the legality of Trump’s actions is a very straightforward principle of constitutional law: Before the president can take any action, he has to have the legal power to do it. Presidents get their power from one of two places: the Constitution or a law passed by Congress. So that no one has to guess at the legality of a president’s actions, executive orders usually start with citing which specific provision of the Constitution or which specific act of Congress gives the president the power to issue that order.

The most troubling executive orders to come out of this administration thus far are those that are deeply vague about what power the president is actually exercising. What concerns those of us who care about preserving the Constitution’s separation of powers most is that this reflects a truly unprecedented understanding of executive power. It is as if the administration takes the view that this president need not be limited by law — that Trump’s presidency comes with the power to do anything he wants.

Basic government civics teaches us that’s just not the way the Constitution works. Congress has the power to make laws and the president has the duty to execute the laws Congress passes. The most basic kinds of laws Congress passes are those directing when and where the government is going to spend money. This power of the purse is the first congressional power listed under Article I of the Constitution. When Trump asserts the power in some of these executive orders to pause or cut off federal spending that Congress has already authorized, he is not acting on executing those laws. He is seizing power the Constitution clearly gave to Congress and Congress alone.

Some of Trump’s other executive orders raise questions of power a bit more complicated than that. For nearly a century, the Supreme Court has upheld laws passed by Congress that prohibit the president from firing the leaders of certain agencies, like the Federal Reserve, without good cause. This is supposed to help preserve some room for expert decision-making by those agencies that is not wholly driven by partisan politics. However, conservative legal advocates since the 1980s have argued that those cases are wrong. They argue the president is a “unitary executive” with the power to control all personnel and policy within the executive branch, no matter what Congress says.

Support in the Constitution for this sweeping unitary executive theory has always been weak. More important, whatever the president’s views of the theory, it is simply not currently the law. That is why the president faces so very many cases against him in the courts. Trump may think the presidency carries with it the power to do whatever he wants, but as we are watching play out in real time, how much power the president has is not just up to him.