Complex sentence: It was a proposed amendment to the California three-strikes law (implemented in 1994 with Proposition 184) that would have required the third felony to be special violent and/or serious crimes to mandate a 25-years-to-life sentence.
Split into simpler sentences: It was a proposed amendment to the California three-strikes law (implemented in 1994 with Proposition 184). Prop 66 would have required the third felony charge against a suspect to be special violent and/or serious crimes to mandate a 25-years-to-life sentence.