(CNN) US attorneys are charged with the power to "prosecute for all offenses against the United States" in their respective federal districts. They may be Department of Justice employees, but they are supposed to maintain independence and discretion within their jurisdiction .

Not every US attorney shares the prosecutorial and other goals of the attorney general and the President. There's an easy way for a President to remedy this difference of opinion, though: he can simply fire US attorneys until he finds ones who happen to agree with him.

For job security alone then, there's tremendous incentive for a US attorney to "happen" to agree with a presidential administration on major law enforcement issues. Of course, for the rest of us citizens, it raises a concern: How can US attorneys impartially prosecute the law if they know the boss is a politician who can fire them?

Attorney General Jeff Sessions asked for the resignations of 46 US attorneys , via a Justice Department announcement on Friday afternoon.

The drama heightened on Saturday afternoon when Preet Bharara, US Attorney for the Southern District of New York, tweeted that he did not resign, that he was fired.

As impolite as it seems, demanding resignations from US attorneys is actually standard operating procedure in the DOJ when a new administration assumes power. Historically, Presidents clear out almost all the US attorneys from the prior administration. President Bill Clinton appointed 80 new US attorneys in his first year of office, out of 93 posts. That's definitely a housecleaning.

Being a US attorney is definitely "at will" employment , in a sense. Each is appointed by the President, with the advice and consent of the Senate.

The appointment is for a four-year term, and each attorney is also potentially subject to removal--but only by the President. The attorney general acts as their supervisor, but he alone cannot terminate them. And while US attorneys' offices are technically distinct entities from the DOJ, they depend upon the Justice Department for financial support and policy creation.

But a US attorney being fired instead of resigning? That's a big difference. It's also very rare. Sometimes there's a good reason to fire a US attorney. Like if he leaks information about an undercover investigation ... to the person being investigated.

In the late 2000s, there was a huge controversy when the George W. Bush administration summarily dismissed eight US attorneys , with no allegations of serious misconduct.

In the politically-charged aftermath, Attorney General Alberto Gonzales resigned , and this remains a rare instance of a mass dismissal of US attorneys by a President, without any concrete grounds.

So a firing like Bharara's is unusual.

Bharara is a superstar among US attorneys, and the man who "struck fear into Wall Street and Albany."

However, Bharara's firing might not have been an act of disrespect by the Trump administration. Rather, it might have been an act of defiance—or more appropriately—civil disobedience by Bharara, who refused the request by Sessions for him to resign.

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It's a clever chess move by Bharara: force the firing, make the administration look like the tyrants. It's not like it hurts Bharara; this is one legal luminary whose job prospects will not be harmed by being "fired" from his last job. As CNN Legal Analyst Paul Callan observed, former US attorneys from this district have even ascended to the New York City mayor's office after their tenure.

The problem is this: because of the massive power US attorneys have over every aspect of our lives, these forced resignations are particularly suspect if they appear motivated by improper political purposes.

On one hand, demanding mass resignations is part of the change in administration. US attorneys know this when they accept the job, which they obtain through the sponsorship of powerful politicians -- in Bharara's case, Sen. Charles Schumer. If forced to resign, most of them will head off to tony white-shoe law firms or don the robe as federal judges.

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On the other hand, sacking US attorneys can look really fishy too. US attorneys need to be impartial . Knowing that their job security is dependent upon the prevailing political winds could affect their judgment.

A prime example is if a US attorney needs to investigate the very administration that appointed him, or the Justice Department that supervises him. What would any of us do if we were faced with two options: investigate and prosecute a foreign terrorist organization ...or our own boss at the Justice Department? The terrorist isn't going to give me a pink slip or ruin my career advancement opportunities.

The role of the US attorneys is to "watch" the "watchmen" in the other branches, including their own executive branch. But our system does allow for a powerful, unacknowledged presidential "veto,": firing US attorneys until the only ones on the job evince an "independent" judgment that just happens to be identical to that of the President.