9:45 AM PT -- Clinton got sprung. He posted bail, and is scheduled to be in court in September.
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.