Roger Clinton -- DUI Arrest in California ... impeccable timing

Hillary Clinton’s brother-in-law is sitting in a jail cell after getting busted for DUI in Southern California … just 2 days before the crucial CA primary vote.

Law enforcement sources tell TMZ … Roger Clinton was arrested Sunday just after 8 PM in Redondo Beach. He was booked for driving under the influence, and we’re told he refused blood alcohol testing.

Roger remains in police custody. His bail is set at $15,000.

Clinton was also arrested for DUI in 2001. That same year, President Clinton infamously pardoned his half-brother for a drug charge.

Unless he bails out before Tuesday … there goes one vote for Hillary.