Habitual offender

The fundamental mistake of the plaintiff in error is his assumption that the judgment below imposes an additional punishment on crimes for which he had already been convicted and punished... The statute under which it was rendered is aimed at habitual criminals; and simply imposes a heavy penalty upon conviction of a felony committed in Massachusetts since its passage, by one who had been twice convicted and imprisoned for crime... The punishment is for the new crime only, but is the heavier if he is an habitual criminal. ... The statute, imposing a punishment on none but future crimes, is not ex post facto. It affects alike all persons similarly situated, and therefore does not deprive anyone of the equal protection of the laws.