Harvard absolutely has courses taught from a book. I’m sure Mankiw requires his textbook for Harvard’s intro econ course. He wrote it, he thinks it’s good.
"THE IMF CONFIRMS THAT 'TRICKLE-DOWN' ECONOMICS IS, INDEED, A JOKE"
> INCREASING THE INCOME SHARE TO THE BOTTOM 20 PERCENT OF CITIZENS BY A MERE ONE PERCENT RESULTS IN A 0.38 PERCENTAGE POINT JUMP IN GDP GROWTH.
> The IMF report, authored by five economists, presents a scathing rejection of the trickle-down approach, arguing that the monetary philosophy has been used as a justification for growing income inequality over the past several decades. "Income distribution matters for growth," they write. "Specifically, if the income share of the top 20 percent increases, then GDP growth actually declined over the medium term, suggesting that the benefits do not trickle down."
"Causes and Consequences of Income Inequality: A Global Perspective" (2015)
I'll add that we tend to overlook the level of government spending during periods trickle-down economics and confound. Change in government spending (somewhat unfortunately regardless of revenues) is a relevant factor.
Let's make this economy great again? How about you identify the decade(s) you're referring to and I'll show you the tax revenue (on income and now capital gains), federal debt per capital, and the growth in GDP.