Catholic Irish emigrants and their subsequent generations to the States were always Democrat supporters right up until Reagan, when they would have switched a bit! Many US city governments including Tammany Hall, Boston and Chicago were controlled by Irish political dynasties, a murphia if you will, which were almost always Democrat based. I've read there may well have been as many as 50 major American cities like this!
Protestant Irish Emigrants tended to support the Republicans!
The Irish -Americans are generally taken as the biggest ethnic origin group in the US, though now much much diluted and the catholic Irish the most economically successful, due to a genius for politics and organisation, despite this the Irish back home cannot plan for anything!