Former Arizona sheriff Joe Arpaio, a convicted criminal and Donald Trump devotee who opened a sweltering outdoor "Tent City Jail" and gained notoriety for dressing inmates in pink underwear, is known for imposing controversial punishments.

Soon, the anti-immigration crusader could be known for a presidential controversy.

President Trump hinted Tuesday that he would make Arpaio the first offender under his presidency to receive a presidential pardon, following the former Maricopa County lawman's conviction for defying court orders not to racially profile for undocumented immigrants.

Granting clemency would be unusual in the modern era given the timing. Just on July 31, a federal court found Arpaio guilty of criminal contempt, a misdemeanour carrying a possible six-month jail sentence.

On Tuesday, Trump told a Phoenix rally that "Sheriff Joe" was "convicted for doing his job." He teased the idea of clemency: "You know what? I'll make a prediction: I think he's going to be just fine."

Arpaio Pardon

Trump joins Arpaio, then a sheriff, during a news conference in Marshalltown, Iowa on Jan. 26, 2016. Arpaio, an anti-immigration crusader, has been a political supporter of the president. (Mary Altaffer/Associated Press)

The president has the uncontested authority to pardon anyone at any time, possibly preventing Arpaio from going behind bars. But doing so in this case would amount to an extraordinary use of presidential clemency powers, according to experts on the pardons process.

Here are a few reasons they cite:

It immediately overturns a federal ruling

Critics argue that delivering a pardon so soon after Arpaio's conviction smacks of a president undermining a federal court decision.

The American Civil Liberties Union says that with such a move Trump would be thumbing his nose at the judiciary and would "undo a conviction secured by his own career attorneys at the Justice Department."

"We have to consider the recency," says William Howell, an expert on presidential powers at the University of Chicago. Pardons may be issued if new information or evidence is found about a case, leading one to reconsider a judicial decision.

Trump is free to issue pardons "even 10 seconds after a conviction," Howell says.

"But when it's back-to-back like this, it's clear there's no new information per se. It's rather a belief that the judiciary simply got it wrong and a correction is needed."

It appears to be about political points

Thousands of people seek pardons. The public has never heard of most of them and never will.

"The Arpaio thing is a cause celebre thing, which makes it more problematic," says P.S. Ruckman, editor of the Pardon Power blog and a law professor at Northern Illinois University. "It sends the false signal that only famous people who have media support can get pardoned, but there are hundreds of people waiting 10 or 15 years who would be highly demoralized."

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After becoming president in 1974, Gerald Ford granted his predecessor Richard Nixon a pardon for any crimes he might have committed during the Watergate scandal. (Associated Press)

In 1974 there was another quick presidential pardon, when Gerald Ford pardoned his predecessor Richard Nixon, just a month after assuming the Oval Office, for the Watergate scandal. Ford declared the pardon covered "all offences against the United States which he, Richard Nixon, has committed or may have committed or taken part in."

Ford defined his motivation: "The tranquility to which this nation has been restored by the events of recent weeks could be irreparably lost by the prospects of bringing to trial a former president."

But there's a big distinction between that kind of pardon and the kind that Stanford University criminology professor Robert Weisberg believes Trump will grant.

Ford made his decision for "political reasons," he says; Trump appears to be pursuing "political gain."

"Ford felt the body politic as a whole would be healthier if it weren't embroiled in a legal battle over Nixon," Weisberg says, noting that the reasoning was framed as being in the best interests of the country.

Arpaio is a "hero of the alt-right" voter base that supports Trump, Weisberg says, but the former sheriff's crime doesn't match the gravity of a national burden that must be exorcised. Instead, Weisberg says, "Trump is almost announcing that he's doing this simply for political grandstanding."

It's early in this presidency

Howell notes that it's also rare in the modern era for pardons to be issued so early in a presidency. Barack Obama waited more than 600 days to issue his first pardons, as did George W. Bush. Trump has just passed his 200th day in office, but it's rare for pardons to be issued in the first year.

Presidents typically reserve the bulk of their pardons or commutations of sentences for the end of their term, when they need not worry so much about political fallout, Howell says.

It ignores Justice Department rules

Under Department of Justice guidelines, convicts are advised to apply for pardons in most cases after waiting five years. The passage of time allows them to show they've transformed their lives and accepted responsibility for wrongdoing, or for new evidence to come to light.

"Which of course Arpaio has not done in any way," said a former lawyer in the Justice Department's office of the pardon attorney, speaking on condition of anonymity.

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Immigrant inmates show off pink underwear while sitting on a bunk in the Maricopa County "Tent City Jail" in 2013. Arpaio gained notoriety for imposing unusual punishments. (John Moore/Getty Images)

It's the norm for the pardon attorney to first at least review the case.

But judging by the apparent lack of a pardon attorney in place for the Trump administration, the former Justice Department staffer said the president "has clearly not shown any interest at all in clemency and the whole pardon authority, except when it's somebody who has a personal friendship" with him.

The pardon attorney job does not require presidential appointment. "To the best of my knowledge, they haven't even posted the position."

The Department of Justice did not respond to a request from CBC News seeking clarification on whether a pardon attorney has been hired.

Arpaio's offence is 'trivial' 

That Trump would intervene in pardoning what Weisberg calls a relatively "trivial" misdemeanour is "extremely unusual," he said, because pardons typically target cases involving years-long sentences.

Arpaio's conviction for contempt of court brings a maximum sentence of six months, which the 85-year-old likely wouldn't have to serve in full, given his age.

The violation involves Arpaio's defiance of a 2011 court order to cease immigration patrols that violated constitutional rights. His office nevertheless continued to stop and detain suspected undocumented immigrants via racial profiling of Latinos.

"So Trump would be engaging in an in-your-face to the judicial system," Weisberg said.

While he said it's arguably an "insult to the judge who ran the trial" when somebody is pardoned after a conviction, the prospect of Trump backing Arpaio over a judge's ruling the former lawman brazenly ignored "takes it to an extra level" of insult.

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Actress Pamela Anderson joins Arpaio as they serve a vegetarian meal to inmates at the Maricopa County Jail in 2015 in Phoenix. People for the Ethical Treatment of Animals lauded the event as 'the first all-vegetarian meal in our nation’s jails.' (Ross D. Franklin/Associated Press)

To Thomas Saenz, president and general counsel of the Mexican American Legal Defence and Educational Fund, a pardon by Trump would be a "gratuitous blessing" of someone who has violated the rule of law and a validation of bigotry.

"He would be blessing unconstitutional racial discrimination against Latinos, and on top of that, blessing defiance of the federal courts," Saenz said.

"It's pandering to what Trump perceives to be a portion of his base. And it's a tremendous step backwards."