In Mr. Herbert Croly's 'Promise of American Life," the most profound and illuminating study of our National conditions which has appeared for many years, especial emphasis is laid on the assertion that the whole point of our governmental experiment lies in the fact that it is a genuine effort to achieve true democracy—both political and industrial.
Croly is widely credited as being the actual source of "The New Nationalism", thus having pulled Theodore Roosevelt even further down the rathole of progressivism. This topic, however, has become somewhat of a point of debate among historians.
A month after Croly's passing, Walter Lippmann, the Father of Modern Journalism, wrote this about his TNR co-founder's influence:
Croly had, I think, made articulate for Roosevelt his aspiration to combine the social and political reforms initiated by Bryan and La Follette with a Hamiltonian affection for a strong national government.
Roosevelt was incredibly influenced by Croly's book The Promise of American Life. Roosevelt made it quite clear by his own hand, and historians other than myself have widely written about it as well as many commentators. Judge Learned Hand wrote in private correspondence that he personally sent a copy to Roosevelt. The only question that remains is what rests in the middle, the how and where. Some historians believe that Roosevelt read Croly's book while out on a hunt in Africa.
Matthew Josephson, a journalist and author of the book The President Makers, shared this curious anecdote: (page 369)
In the trunks that went to Africa there had been placed by chance a copy of Herbert Croly's The Promise of American Life, published early in 1909.
In his writing, Josephson seems to indicate that Colonel House placed this particular copy there instead of the copy that Learned Hand made clear that he sent. Which leaves open a debate for whether or not Roosevelt received two copies, did Josephson get it wrong and the copy that went to Africa was the one that Hand sent? It's probably impossible to confirm that level of minutiae, whatever may be the case in this instance.
But we do know two things for certain. First, that Roosevelt wrote about the personal impact of Croly's book Promise of American Life as well as another of Croly's books, Progressive Democracy.