This is an absolutely _wild_ take. What "leftist" positions are you referring to? Be specific.
"Most of the federal government’s authority over the economy derived from a clause in the Constitution empowering Congress to regulate interstate commerce, but the court construed the clause so narrowly that in another case that next spring, it ruled that not even so vast an industry as coal mining fell within the commerce power."
The "regulation of interstate commerce" now is a joke of a catchall which basically is modernly interpreted as "government can damn do what it pleases in every avenue of our lives" from its original interpretation which was "you can make sure horses can get from point A to point B".