We’re backstage at Dublin’s Smock Alley Theatre and Pearse Doherty is making me a cup of tea. The Donegal TD has just taken part in the launch of Sinn Féin’s election manifesto along with front-bench colleagues. The party’s finance spokesperson appeared as the stern guardian of the purse’s strings as the only man on stage wearing strict business attire including a tie. The manifesto provides for €17.2 billion in additional current spending, €2.9 billion in net tax cuts and €41.8 billion in new capital investments over the next five years if voters decide that he will be the next minister…