I know that ideological biases require leftists to discredit any and all instances where a supply-side approach seemed to have worked……but that’s ideology.
I’m a political & economic liberal, not a leftist. Ideology influences everyone to some degree, but I find that empiricism (i.e., being data-driven) serves as a useful check on bias. There is plenty of evidence that supply-side approaches often work. Harding & Coolidge were relatively responsible; they cut taxes to stimulate the economy, while cutting public spending to reduce the national debt. They failed, however, to use the tools the Progressives left them (e.g., Federal Reserve, the FTC, ) to regulate banks & businesses properly.
LBJ was also relatively responsible, signing a tax cut stimulus in 1964, but then slapping on an income tax surcharge to bring the budget back into balance in 1968. Because he didn’t back off on regulation, no crash came on his watch, or even during Nixon’s first term.
When you combine tax cuts with underregulation (Reagan, Bush the Younger), you get the S&L Crisis & the 2007 meltdown. Worse, “starve the beast” fiscal irresponsibility makes it harder to prime the pump when those crises hit.
As the Depression deepened, Hoover did intervene — more than any previous president, but still not enough to turn the tide. (Smoot-Hawley did not help.) FDR intervened significantly more, with positive but limited results. Only with World War II did we become true Keynesians, spending whatever it took to become the arsenal (& breadbasket) of democracy. FDR’s free trade agreements promoted recovery before, during and after the war, and should be considered part of the New Deal.