E.g. If Sinn Fein were to win in both Ireland and Northern Ireland.

I know the Ba'ath party controlled both Iraq and Syria, but was its hierarchy always split or was it once one large party that spanned borders?

In terms of governing, I'm not thinking along the lines of the Communist parties that governed the Soviet bloc since they were all nominally independent or separate, right? I'm interested in parties like Sinn Fein that're formally a single organization.