Michael Cohen Looks Somber Arriving to Prison for 3-Year Sentence

Michael Cohen's got the Monday blues on steroids ... he just checked himself into prison to begin his 3-year sentence -- but on the positive(ish) side he can hang with The Situation from "Jersey Shore."

President Trump's former personal attorney was spotted Monday arriving at the Federal Correctional Institution in Otisville, NY ... where he'll be incarcerated after pleading guilty to tax fraud and campaign finance violations.

As we reported ... Cohen was slapped with 8 federal charges in August 2018. The campaign finance violation was for his $130k hush payment to Stormy Daniels in the 11th hour of the 2016 election.

Before heading off to the minimum-security prison -- considered a haven for white-collar criminals and 70 miles away from his NYC crib -- Cohen told reporters outside his pad "there still remains much to be told and I look forward to the day when I can share the truth."

Cohen also appeared to take a shot at Trump ... saying by the time he's released he hopes "the country will be in a place without xenophobia, injustice and lies at the helm."