Racism is not left or right. It is seperate from politics.
It is certainly used by politicians for their own personal gain. As such, it is always left-wing regardless of which party is trying to use it.
That said, it is the Democrat Party that historically has engaged in widespread use of racially motivated politics - including present today.
The Democrats started the Ku Klux Klan, imposed segregation, poll taxes, etc.
Margaret Sanger of Planned Parenthood fame wanted to wipe out blacks, hence abortion clinics in black neighborhoods - the Nazis even borrowed strategy and rhetoric from her.
Racist Democrat Woodrow Wilson screened the racist film Birth of a Nation in the White House. The Democrats motivation for launching a war on marijuana in the 1930's was so they could target blacks.
It was the Democrats who worked to block the Civil Rights Act. After that eventually passed, the Democrats shifted gears for political expediency and embraced race hustlers MLK, Jesse Jackson, Al Sharpton, John Lewis, John Conyers, Maxine Waters, etc.