To understand the background to the latest row in the Labour Party over its public spending plans, the best place to start is not in Westminster or for that matter the UK – but on the other side of the Atlantic. There was a reason the shadow chancellor Rachel Reeves decided to launch her latest economic strategy in the US rather than in the UK: it owes rather a lot to what Joe Biden and his treasury secretary, Janet Yellen, are doing right now. They have implemented a set of policies which are arguably the most important economic legislation in…