President Donald Trump recently attempted to fire Gwynne Wilcox, a member of the National Labor Relations Board (NLRB) and its former chair. This attempted termination is just one of many similar actions Trump has taken, but it is also a singularly important move by Trump because it could trigger a legal fight that could significantly expand the powers of the presidency.

Most federal agency leaders and similar officials can be fired at will by the president. But federal law provides that members of the NLRB, like top officials at a number of similar agencies, may be removed “for neglect of duty or malfeasance in office, but for no other cause.” So, unless Trump has evidence that Wilcox ignored her duties or engaged in misconduct, this law forbids him from removing her until her term in office expires.

However, much of the federal judiciary — including all of the Supreme Court’s six Republicans — subscribes to a legal theory known as the “unitary executive,” which raises serious doubts about whether Congress can give this kind of job security to an official like Wilcox. In its strongest form, the unitary executive gives the president control over every federal government job that isn’t part of Congress or the judiciary — meaning he can hire and fire at will — although it is unclear whether any of the justices would take this theory that far.

If Wilcox decides to challenge Trump’s decision to fire her, that is likely to trigger one of the most consequential legal fights of Trump’s two terms in office. Even if she doesn’t, Trump’s administration appears ready to fire so many federal officials that a legal showdown over the unitary executive is almost certainly inevitable. If Trump prevails in that contest, he would not simply gain the power to decide how labor law is enforced, he will also gain unprecedented power over agencies like the Federal Reserve that have the power to reshape (or ruin) the US economy.

These firing disputes, in other words, could be one of the most significant milestones toward converting Trump from a public servant into a king.

So what, exactly, is the unitary executive?

The idea of a unitary executive begins with a seemingly innocuous passage of the Constitution, which states that “the executive power shall be vested in a President of the United States of America.” As proponents of the unitary executive point out, and as Justice Antonin Scalia put it in a famous dissenting opinion, this provision “does not mean some........

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