The tragedy of Joe Biden is that people see his age, his frailty and his ailing poll numbers and they miss the bigger story. Which is that his has been a truly consequential presidency, even a transformational one. In less than three years, he has built a record that should unify US progressives, including those on the radical left, and devised an economic model to inspire social democratic parties the world over, including here in Britain. Sadly for Biden, politics and government are different things: it takes more than a record of good governance to get reelected. For one thing,…