Article II, Section 2, Clause 1, of the US Constitution gives the President of the US the power to grant Reprieves and Pardons for offences against the United States, except in cases of impeachment. It is one of the least limited powers of the President. This is how he can do it... now for the who.
Do you know Sheriff Joe Arpaio? He is 85 years old. He served in the US Army from 1950-1954. He was a Police Officer in Las Vegas Nevada in 1957, transitioned into the Drug Enforcement Administration where he was stationed in Turkey, Argentina, and Mexico, then became the head of the DEA in Arizona for 25 years. He was elected Sheriff of Maricopa County, Arizona six times from 1992 to 2017. He was known as America's Toughest Sheriff. When you went to jail in Maricopa County... it was less likely you would ever be back in jail in Maricopa County ever again. Sheriff Joe did not run a fun place to be. The people of Arizona elected Sheriff Joe because they wanted him, and an end to the illegal immigration problem. Sheriff Joe was very effective at his job. Democrats, Progressives, Socialists, and every other group on the left, hate Sheriff Joe Arpaio. It was a political hit job, and this man that has dedicated his life to Law Enforcement and the protection of the American people, should never be persecuted this way.
I met Sheriff Joe in 2010. He's a very funny man with a lot of juicy stories to tell. We should build a monument and we need many more just like him. If I can accept Obama's pardon of Bradley Manning... which was appalling... then this should not be a problem.