One case illustrates the unique challenges facing the Trump administration in reforming a broken immigration system.

Constantino Banda-Acosta was arrested in May on DUI charges related to a hit-and-run crash that severely injured a 6-year-old boy in California. The 38-year-old illegal immigrant from Mexico had been deported 17 times since 2002, federal records show.

Yet, despite Banda-Acosta’s DUI arrest and others for domestic violence, the U.S. Attorney's Office refused to prosecute him for “criminal re-entry” after deportation. As a low-level criminal alien, Banda-Acosta met the guidelines of President Barack Obama's "prosecutorial discretion" policy.

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That policy backfired May 6, when Banda-Acosta, allegedly driving drunk and speeding, slammed his vehicle into the Lake family -- driving home from a day at Disneyland.

Banda-Acosta left the scene, but was stopped a mile away in his damaged pickup by the Border Patrol near San Diego. He left 6-year-old Lennox Lake unconscious and without a heartbeat on the pavement. With the help of his parents and paramedics, the boy survived.

Yet, based on federal court records, this is the first time U.S. prosecutors charged Banda-Acosta with a federal immigration violation, despite having multiple chances to put him behind bars for 5 years or more at various times.

"This is yet another harrowing example of why immigration enforcement is critical to the rule of law and safety of American citizens," said Sen. Charles Grassley, R-Iowa. "When someone is able to re-enter the country after being removed [17] times and puts the life of a child in jeopardy, it should be a wakeup call to all of us that border security and enforcement of our laws must be a priority to ensure safety and justice in America.”

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Grassley has asked the U.S. Department of Homeland Security to investigate the case and explain how the Trump administration would handle it differently.

A look at Banda-Acosta's record, provided by U.S. Immigration and Customs Enforcement, shows him stopped multiple times while trying to gain entry using counterfeit documents, and trying to sneak past the Border Patrol. But it also reveals for every time he was stopped, he somehow got through. And when arrested for crimes allegedly committed in the U.S., while the San Diego County Sheriff honored ICE detainer requests, the U.S. Attorney failed to file federal charges requiring jail time.

Number of times Constantino Banda-Acosta has been deported:

? 11/12/2002 – Removed to Mexico via the Tecate Port of Entry based on an expedited removal order issued.

? 2/9/2003 – Removed to Mexico via the San Ysidro Port of Entry based on an expedited removal order after Banda attempted to illegally enter the U.S. using counterfeit documents.

? 1/8/2004 – Removed to Mexico via the Calexico Port of Entry after Banda attempted to illegally enter the U.S. by presenting a counterfeit alien registration card.

? 7/19/2004 – Removed to Mexico via the Otay Mesa Port of Entry.

? 12/29/2004 – Removed to Mexico via a port of entry in Nogales, Arizona, after Banda attempted to illegally enter the U.S. at the San Ysidro Port of Entry concealed in the trunk of a vehicle.

? 4/8/2007- Removed to Mexico via the San Ysidro Port of Entry after Banda attempted to illegally enter the U.S. by making an oral false claim to United States citizenship.

? 8/24/2007 – Removed to Mexico via the San Ysidro Port of Entry following the reinstatement of a prior removal order.

? 3/12/2008 – Removed to Mexico via San Ysidro Port of Entry.

? 2/16/2009 - Voluntarily returned to Mexico by U.S. Border Patrol agents.

? 6/23/2009 – Voluntarily returned to Mexico by U.S. Border Patrol agents via Yuma, Arizona.

? 1/18/2011 - Removed to Mexico via the San Ysidro Port of Entry after Banda was transferred from the George Bailey Detention Facility to ICE custody.

? 1/22/2011 - Repatriated to Mexico at the San Ysidro Port of Entry after using an entry document belonging to someone else.

? 2/9/2011 - Returned to Mexico at the San Ysidro Port of Entry.

? 3/4/2011 - Removed to Mexico via the San Ysidro Port of Entry after attempting to illegally enter the U.S. by presenting a counterfeit Mexican passport.

? 3/27/2011 – Voluntarily returned to Mexico via Harlingen, Texas. Banda was arrested by U.S. Border Patrol agents after he illegally entered the U.S. on foot.

? 1/10/2017 - Removed to Mexico via the San Ysidro Port of Entry.

? 1/17/2017 – Removed to Mexico via San Luis, Arizona after he was stopped by Border Patrol agents patrolling the border.

"While, obviously, many Americans drive impaired and cause crashes, this one could have been prevented if one of the many immigration officers who dealt with him had imposed greater consequences that would have dissuaded him from coming back," said Jessica Vaughn, with the Center for Immigration Studies. "Between the lack of consequences, the lure of a job, the availability of bogus documents and the gaps in our border security, to this guy our immigration system was a revolving door -- with a welcome mat on our side. And when he faced no consequences for breaking our immigration laws, why would he fear consequences for breaking other laws?"

The Trump administration has promised changes and Grassley hopes they follow through, beginning with Kate's Law, which would mandate a five-year mandatory minimum jail sentence after the second expedited removal order. If that law that been in effect at the time, Bando-Acosta would have been in prison beginning in 2003. Under the bill, any subsequent arrest would have gotten him an even longer sentence.

The law is named for Kathryn Steinle, a 32-year-old woman who was fatally shot in San Francisco in 2015, allegedly by a felon who had been deported but returned to the U.S.

Unlike the “prosecutorial discretion” adopted by the Obama administration, new Attorney General Jeff Sessions has ordered prosecutors to "charge and pursue the most serious, readily provable offense" in all cases, including immigration crimes.

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"People who re-enter, after being convicted of committing a crime, they get deported and come right back," Sessions said last week in Tennessee. "So you just can't deport them again. They have to be punished and that sends a message more and more that you shouldn't come back. And if we build a wall, then they're not coming back."

In his letter to Department of Homeland Security Secretary John Kelly, Grassley is demanding to know if Acosta, charged with a second DUI, would qualify for priority deportation. Although there is still no certainty, despite the charges, that ICE will ever get its hands on him again.

Under current California law, if Banda-Acosta makes bail, he will not be held for deportation. California requires at least one felony conviction. Being charged with felony hit-and-run doesn't qualify. And unless ICE knows of his release, there is no certainty they would be in place to pick him up at jail for deportation.