As the scandal of Katherine Zappone’s UN appointment ebbed last week and Mary Robinson scolded him about climate change, it left Leo Varadkar contemplating a historic gladiatorial showdown with Mary Lou McDonald. The Tánaiste will probably shrug when friends tease him about his troubles…but then there’s another woman in Brussels he has to think about. But that epic confrontation with the Sinn Fein leader will be the narrative for the next general election, probably in 2025, and that could well reconfigure party politics in Ireland for a generation. That momentous dual with Mary Lou may also define his life through…