OK let's use Johnathan Chait's chart on tax revenue

Johnathan Chait thinks we can sustain federal revenues above 19% of GDP.    Look at his chart, we have never kept revenues above 19% for more than a couple of years, an election cycle mainly.

What is Johnathon Chait's issue?  Because we managed to sustain high income for a couple of years we should plan on doing is for five-ten years, then bet the economy on the idea?