Cedric L. Alexander is a CNN law enforcement analyst and deputy mayor of Rochester, New York. He is a former president of The National Organization of Black Law Enforcement Executives. The views expressed are his own.

(CNN) "The worst part is that people got hurt," a seventy-year-old man caught up in the Charlottesville clashes told the Washington Post. "The police stood by and didn't do a g------- thing." Experts as distinguished as former Philadelphia chief Charles H. Ramsey commented on that department's failure to "have overwhelming force" on hand, and others spoke of the police appearing "outnumbered, ill-prepared and inexperienced."

As a former law enforcement executive and the current deputy mayor of Rochester, New York, I am deeply anxious about the rallies extreme far-right groups are planning in cities across the country this weekend. My concern is that the police in at least some of these cities will find themselves in the same horrific predicament the Charlottesville PD faced on August 12.

In times of hazard, the police are the primary point of contact between the government and the public -- victims, prospective victims, perpetrators, and prospective perpetrators of violence alike. Quelling a riot is hard and dangerous work, but the even greater challenge is to "be the government" when everything is chaos.

What Charlottesville needed most urgently was the full embrace of their government. The most difficult and demanding police mission is to provide that embrace, and in my estimation, the Charlottesville department fell short and must accept a share of the blame.

But not the lion's share.

In responding to each call for help, a police force brings the policies and values of both the local and national government to bear. In Charlottesville, we saw the grave danger both the police and the community face when the government's very highest authority, the President of the United States, fails to live up to the duties of his office.

In Charlottesville, I believe, this failure contributed to injury and tragic loss of life. It degraded the performance of the police force. My fear is that something similar could happen again this weekend on a larger scale.

I do not mean to say that President Trump has not aired opinions -- some vague, others inflammatory, many inconsistent and self-contradictory. I do mean that he has time and again failed to articulate unambiguous policies and values. The pronouncements that routinely issue from this White House are almost always supremely incoherent.

To many, they are also evasions conveyed through figurative winks and nods. Speaking to police on Long Island on July 28, Trump encouraged a policy of brutality. "When you guys put somebody in the car and you're protecting their head, you know, the way you put their hand over? ... I said, you can take the hand away, okay?" Police leaders nationwide pushed back and denounced brutality. But the presidential eye had already winked and the head already nodded.

Laws cannot be enforced and communities cannot be protected this way. Mixed messages from President Trump put in jeopardy the police as well as the communities they serve. At the very least, they lead to a degree of paralysis among first responders. At the very worst, they condone unnecessary force. Either way, lives are put at risk.

President Trump has not confined mixed messages to law enforcement; his winks and nods have also been directed toward proponents of white supremacy and white nationalism. He has given us government by innuendo. Who can blame a police department for an inability to enforce innuendo?

The tragedy of Charlottesville is that, this time, the innuendo encouraged domestic terrorists. What will happen this weekend?

All police officers swear an oath to uphold the Constitution. It is too often a most difficult duty to perform, especially in situations like Charlottesville, when the First and Second Amendments come into conflict.

While the rights guaranteed by the Constitution are absolute, putting them into practice very often cannot be. Both common sense and common morality (as well as judicial ruling) say we cannot use free speech to yell Fire! in a crowded theater that is not burning. And our right to "assemble" is governed by the adverb "peaceably." Assault with fists, pepper spray, improvised spray-can flamethrowers, baseball bats, and automobiles do not constitute free speech or assembly. We have the right to bear arms, and, in Virginia and a number of other states, the right to carry them openly. But do those marching with assault rifles (per the Second Amendment) broadcast to the police and the community an intention to assemble "peaceably" (per the First Amendment)? And should the police do nothing until, armed as they are, their true intention is revealed?

Police leaders and officers are called on to make Constitutional judgment calls all the time. Making these is far more difficult when the only messages sent from the top are winks and nods -- mostly toward the extreme right.

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We don't know how the President feels about these upcoming rallies, but former KKK Grand Wizard David Duke has been very clear about his own feelings toward the President. "Thank you President Trump for your honesty & courage to tell the truth about #Charlottesville & condemn the leftist terrorists in BLM/Anitfa."

The rest of us are still waiting for the President to deliver something more than his stunning equation of armed Nazis, white supremacists, and anti-Semites with those who stood up to oppose them in Charlottesville. Donald Trump proclaimed himself the "law and order candidate" and was duly elected. But how can you be the law and order President if you cannot tell the difference between right and wrong?