Editor's note: Ruben Navarrette Jr. is a CNN.com contributor and a nationally syndicated columnist.
San Diego (CNN) -- I bet it sounded like a good idea at the time. Now, not so much.
"It" was the ill-conceived decision by GOP presidential hopeful Rick Perry to hitch his wagon to the clownish Arizona Sheriff Joe Arpaio, an opportunist who in recent years has taken to rounding up illegal immigrants and parading them outside his jail to catch the attention of television cameras.
How did Perry get mixed up with that circus? Simple. The Texas governor got into a political scrape, and made the mistake of overcompensating. He was looking for quick validation from his party's nativist fringe because he had gotten hammered by GOP rivals for signing, in 2001, a reasonable bill in the Lone Star State that allows illegal immigrants who go to college to pay what other residents pay: in-state tuition.
In fact, Perry didn't just sign that bill. He defended it and defiantly said he'd sign it again. Worse, in one debate, he told Republicans who disagreed with the measure that they didn't "have a heart." Good for him.
Yet, after that, his poll numbers plummeted.
In a futile attempt to get them up again, Perry underwent a radical makeover. He said that, if elected president, "My policy will be to detain and to deport every illegal alien that we apprehend."
Ah, governor, you mean the ones you're not helping put through college?
Perry even did penance by making a pilgrimage to the desert where he asked Sheriff Joe for his support. He got it. Just a few weeks ago, Arpaio announced he was endorsing Perry and he even went to New Hampshire to help him campaign.
"The federal government has failed on border crime and border enforcement, and no candidate for president has done more to secure the border than Governor Rick Perry," Arpaio said in a statement. "I'm endorsing Rick Perry because we need a tough-on-crime president who will champion and fund full-time border security operations from Brownsville to San Diego."
Now, America's toughest sheriff is busy fending off allegations of discrimination and racial profiling. Such is the result of a three-year investigation by the U.S. Department of Justice into Arpaio and the Maricopa County Sheriff's Office. At issue: their clumsy handling of something they never had the know-how or skills set to do: immigration enforcement.
The DOJ's report packed a punch. It accused Arpaio's office of maintaining a "pervasive culture of discriminatory bias against Latinos" that "reaches the highest levels of the agency."
It accused the sheriff's deputies of routinely engaging in "unconstitutional policing" that includes racially profiling Latino drivers, illegally detaining and arresting Latinos and carrying out military-style immigration patrols sparked by racially tinged citizen complaints. It said that inmates in the county jails who don't speak English are often punished and denied critical services. Finally, it also charged that the leaders of the agency have an odious practice of using their power to retaliate against critics.
None of this will come as a shock to Maricopa County's growing Latino population, which has been complaining of abuse by Arpaio and his deputies for several years.
Following the report's release, the Department of Homeland Security immediately terminated its 287(g) agreement with the Sheriff's Office and denied it access to the federal databases that it is practically forcing upon other agencies to locate illegal immigrants under the controversial Secure Communities program.
As someone who lived in Phoenix in the late 1990s and wrote columns for the Arizona Republic newspaper, I've known Arpaio and written about him for nearly 15 years. I prefer the original version. Back then, the sheriff said that his office should not waste limited resources enforcing federal immigration law.
By contrast, Joe Arpaio 2.0 seems to take shortcuts that run afoul of the Constitution. Just because a media hungry lawman is hunting for illegal immigrants doesn't mean he can single out Latinos -- including the U.S.-born, some of whose families have lived on this side of the border much longer than Arpaio's ancestors have lived on this side of the Atlantic.
Next, Justice Department officials will try to strike an agreement with Arpaio to implement a plan that fixes what is broken, one that can be enforced by a judge. The officials are giving the Sheriff's Office 60 days to come up with a solution or face litigation.
Those who defend Arpaio and brush aside concerns over racial profiling will likely say that it's appropriate for law enforcement officers to put extra scrutiny on Latinos since most illegal immigrants in the United States are Latino.
The last statement is true enough. But just because most illegal immigrants are Latino doesn't mean that most Latinos are illegal immigrants.
Besides, the opponents of illegal immigration always want to convince us that they're colorblind. That argument gets hard to make when the apologists for racial profiling start defending the idea of singling out people of one ethnicity.
So what did Perry do when the Justice Department report came out? The worst possible thing. He doubled down on his bad judgment. He had already made two mistakes in snuggling up to Arpaio and accepting his endorsement. He went for three by defending Arpaio.
"I would suggest to you that these people are out after Sheriff Joe," Perry told reporters. "He is tough. And again, when I'm the president of the United States, you're not going to see me going after states like Arizona or Alabama, suing sovereign states for making decisions."
Even if those decisions are bad? This is not a good sign for Perry. We need a president who has character and courage, and he showed both of those qualities early in this campaign. But we also need a president with judgment, and the ability to stop and change course when they take a wrong turn.
For Rick Perry, that wrong turn occurred in the Arizona desert, near the intersection of ambition and fear. And now a once-promising candidate has lost his bearings.
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The opinions expressed in this commentary are solely those of Ruben Navarrette Jr.