Why hasn't the growth rate of real potential US GDP recovered?

Missionary Work Among Savages blog, also known as 2slugbait, wrote about whether President Reagan's 1981 tax cuts performed as advertised. I think his motivation was to determine if a similar supply-side approach could have been a better alternative to the fiscal stimulus measures implemented by Federal Reserve governor Bernanke, immediately following the 2008-2010 financial collapse. 

In other words, would a Reagan-type tax cut in 2008 have driven a stronger recovery than we experienced with Obama? The recovery during Obama's second term in office was one of the most anemic in U.S. history.

Supply-side economics maybe not so great?

2slugbaits demonstrates empirically why supply-side economics was only mildly effective. Specifically, neither of the following worked quite as well as Arthur Laffer forecasted:

1. cutting the top marginal tax rate to encourage greater labor effort 
2. supply-side structured tax cuts to encourage more personal savings 

Skepticism about David Stockman and Laffer's economic policy recommendations during the Reagan Administration is only mildly interesting to me. 

The sort of tax cuts that include middle- and lower-income wage earners, not solely high net worth "job creators" 😕😡 CAN provide a modicum of supply-side stimulus! That was apparent from 2017 to March 2020.

Something else is much more interesting to me: The long-term decline in real potential U.S. GDP.

Gold Star of Texas

The state capitol building in Austin, Texas (21 October 2008)

Cupola of the state capitol at Austin

Photograph by TedLandphair via Picasa