According to the RCC is supporting abortion the same sin as having an abortion?
(Not talking about the doctor. But supporters of the act of abortion.)
To be an accomplice to murder (e.g., selling a gun, abortion instruments, etc.) is not necessarily the same as actually murdering. There's a distinction between material and formal cooperation in sin (cf. this article for more info). Material cooperation supplies the means for committing the sin, and formal cooperation assists in the act directly (e.g., two hit-men shooting one person at the same time would be both formally cooperating in the murder). And there are distinctions within material cooperation: proximate and remote cooperation. For example, a nurse handing an abortionist an instrument during his murdering of a child would be proximate material cooperation (some may argue it's formal cooperation) in murder for the nurse (and certainly formal cooperation for the abortionist). A surgical company making instruments that could be used for other purposes than abortion would be a remote material cooperation in the sin of abortion.
Voting for pro-abortion politicians certainly makes one an accomplice in the murders that politician permits.
Also, in the case of abortion, being an accomplice to it and directly performing it are both excommunicable offenses.