"The functions of government are in a very real sense independent of legislation, and even constitutions, because [they are] as old as government and inherent in its very nature. The bulk and complex minuteness of our positive law, which covers almost every case that can arise in Administration, obscures for us the fact that Administration cannot wait upon legislation, but must be given leave, or take it, to proceed without specific warrant in giving effect to the characteristic life of the State." ["Notes for Lectures at the Johns Hopkins," January 26, 1891, Papers of Woodrow Wilson Vol. 7, p. 121]
While FDR is indeed responsible for his own actions like 'Court Packing', he does come from the infamous heritage of the 1880s-1920s Progressivism/Populism. While they were not 'specifically' Socialist or Communist, it is instructive how influenced they were from German & European intellectuals and proposals.
For a LENGTHY treatment on the ancestry of the SWAMP, I recommend this 2007 monograph from Heritage Foundation / Hillsdale College; "The Birth of the Administrative State: Where It Came From and What It Means for Limited Government". The above Wilson quote comes from this paper.
“the desirability of a powerful bureaucracy over squabbling ELECTED politicians”
We have that today in spades, much larger than in the 30s. After all, they have had 80+ years to grow and perfect it.