Page Pate, a CNN legal analyst, is a criminal defense and constitutional lawyer based in Atlanta. He is an adjunct professor of law at the University of Georgia, a founding member of the Georgia Innocence Project, a former board member of the Federal Defender Program in Atlanta and the former chairman of the criminal law section of the Atlanta Bar Association. Follow him on Twitter @pagepate . The opinions expressed in this commentary are his.

(CNN) In what appears to be a brazen, racially motivated attack on a group of counterprotesters in Charlottesville, Virginia, over the weekend, one person died and many more were injured.

On Monday President Donald Trump finally denounced the white supremacists whose demonstration led to the attack -- joining politicians and commentators of all stripes who had already harshly and uniformly condemned the Charlottesville attack as a racially motivated terroristic act.

Even conservative Sen. Ted Cruz has tweeted that the attack should be prosecuted as an act of "domestic terrorism." But Sen. Cruz should know that, because of the way Congress has limited the reach of federal terrorism laws, the driver who plowed his car into the crowd can't actually be prosecuted for terrorism.

Federal law defines "domestic terrorism" as criminal conduct that takes place primarily in the United States and involves "acts dangerous to human life" that appear to be intended to either "intimidate or coerce" a group of people, or to influence government policy through "intimidation or coercion."

Seems pretty clear, right? Wrong. While Congress chose to define "domestic terrorism," it did not actually create a crime of domestic terrorism. The punishment for committing an act of "terrorism" under federal law only covers crimes that either occur outside the United States or are initiated by people outside the United States. That means an act of pure terrorism that occurs right here at home, without foreign involvement, can't be prosecuted as terrorism under the law.

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This is the same problem that federal prosecutors faced in charging Dylann Roof in the Charleston church murders, and Robert Lewis Dear for his rampage inside a Planned Parenthood clinic in Colorado. Those were horrible crimes, and met the definition of "domestic terrorism" under federal law. But they could not be prosecuted as terrorism because the law doesn't allow it.

Of course, this doesn't mean that the federal government can't pursue the Charlottesville attacker. Just like Dylann Roof, the suspect in Charlottesville can and likely will be prosecuted for allegedly committing a federal hate crime . The Justice Department has already opened a federal civil rights investigation. Presumably, that investigation will focus on a possible violation of federal hate crime laws.

To prosecute the driver for a federal hate crime, the government will need to show that this attack was motivated because of the victim's "actual or perceived race, color, religion, or national origin."

Unfortunately, that can be difficult to do in a trial. Federal prosecutors will have to prove that the motive for the crime was based not just on hate, but on a specific type of hate -- racism. The fact that this person may have been associated with groups that promote hatred or racism isn't enough.

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Interestingly, and as a possible preemptive defense to a hate crime charge, the mother of the Charlottesville suspect, James Alex Fields Jr., told CNN affiliate Toledo Blade that she her son was just going to a Trump rally. "I didn't know it was white supremacists. I thought it had something to do with Trump," she said. If this person got so worked up because of his love for Trump that he drove into a diverse group of people, that may be enough to create a reasonable doubt that this killing was motivated by racism.

Even if it were easy to convict this person of a hate crime, that doesn't mean that a prosecution for domestic terrorism wouldn't be a better fit. It's great that the politicians have been vocal in their condemnation for this attack, and for these groups. But talk is cheap. Congress needs to "walk the walk" and do something about this violence and the people that promote it.

Congress needs to fix this law so federal prosecutors have the tools they need to treat groups that promote hate and violence as the terrorists they are. And this is the perfect time to do it.

Don't be concerned that this attack won't be investigated and the person who committed this crime aggressively prosecuted. He is already charged with very serious crimes under Virginia law. But it would send a much more powerful message to groups that support and promote this kind of violence to call it was it is and allow for federal prosecution of these crimes as terrorism.

Until this law is changed, homegrown terrorists like this guy can't be charged as terrorists even though the law is clear that they have committed terroristic acts.

I agree with Sen. Cruz that this horrific, racially-motivated murder should be prosecuted as an act of "domestic terrorism." Unfortunately, unless and until Ted and his colleagues do something to change the law, it can't be.