WASHINGTON — Almost everything about President Trump's pardon of former Arizona sheriff Joe Arpaio was unusual.

Trump chose a politically polarizing anti-immigration sheriff as the recipient of his first pardon — the kind of controversial grant of clemency recent presidents have reserved for the 11th hour rather than their first act.

Arpaio didn't meet the Justice Department guidelines for a pardon. His conviction wasn't five years old, he hadn't expressed remorse and he hadn't even applied to the Office of Pardon Attorney.

The day before, press secretary Sarah Huckabee Sanders said the president would follow a "thorough and standard process" in considering the pardon. That process usually requires seven layers of review and an FBI background check.

More:White House: Trump will follow standard process for Arpaio pardon

Decision:Joe Arpaio says Trump kept him guessing about pardon, too

Related:With Joe Arpaio free, 5 things to know about presidential pardons

No matter. The constitutional authority to "grant reprieves and pardons for offenses against the United States" is arguably the most absolute power a president has.

He has to work with Congress to pass bills, appoint cabinet secretaries or negotiate treaties. But a pardon can be granted with the stroke of a pen — sometimes not even that — and can't be overturned by the Congress or the courts. Once delivered, not even the president himself can take it back.

More:No need for paperwork: Trump could pardon Sheriff Joe Arpaio in a tweet

Despite the absolute nature of the power — or perhaps because of it — presidents are often downright shy about it.

President Harry Truman didn't publicly disclose his pardons. President Gerald Ford pardoned his predecessor, Richard Nixon, on a Sunday morning with no advance warning. President George H.W. Bush pardoned key figures in the Iran-Contra affair only after losing re-election. President Bill Clinton pardoned fugitive financier Mark Rich, two Democratic congressmen, a figure in the Whitewater scandal and his own brother — all on his last day in office.

None of them telegraphed their intentions quite like Trump, who had been openly hinting at the Arpaio pardon for two weeks. "I think he’s going to be just fine," Trump said at a campaign rally in Phoenix on Tuesday. But he said he wouldn't announce the pardon then because it would be too "controversial."

"This is just the most in-your-face gesture imaginable for the pardon power," said Mark Rozell, dean of the public policy school at George Mason University and a pardon scholar. "We're going to pardon someone who hasn’t admitted that what he's done is a crime, and has shown no remorse."

Indeed, President Ronald Reagan refused to pardon the Iran-Contra figures, including Lt. Col. Oliver North, because it would signal that North had done something illegal that needed pardoning. While a pardon can undo a conviction in the eyes of the law, it can also condemn them in the eyes of history.

"From the very beginning I've said that to consider a pardon would leave — even if I did that — would leave them under a shadow of guilt for the rest of their lives," Reagan said the month before he left office.

In pardoning Arpaio — who had been convicted just last month for defying a judge's order to release from jail people suspected of nothing more than an immigration offense — Trump also bypassed 2,270 other pending applications for pardons, most of which have been waiting for years.

Beyond Arpaio — and reportedly figures in the Russia investigation — Trump seems to have shown very little interest in the pardon power. The Office of Pardon Attorney has no director, and Trump has not provided the office with any guidance about how to process its pending cases.

On Friday night, Trump tweeted one of his reasons for the Arpaio pardon, saying the 85-year-old former sheriff "kept Arizona safe." Opponents said he engaged in racial profiling and physical abuse of Hispanic inmates.

P.S. Ruckman Jr., a political scientist who has studied the history of presidential pardons, says Trump's use of a pardon for Arpaio looks more like crass politics than a serious use of an important presidential power.

"This looks more like a stunt," he said. "He’ll get the mileage out of it, and the publicity, and rile up the base."

But after dangling the possibility of a pardon so publicly, he said, "it would be bizarre if he didn't pardon the guy."