Trump says the economy is in “a boom the likes of which we have never seen before.” Actually, we have seen it before, when Barack Obama was president. GDP growth in 2015 was 2.9%, the same as it was in 2018. In the 1990s, by contrast, annual growth rates often reached 4%. Looking only at a graph of growth rates over the past decade, you wouldn’t know the 2017 tax measure had ever happened.