My research for a recent university essay led me to read Populist Nationalism: Republican Insurgency and American Foreign Policy Making, 1918-1925 by Karen A. J. Miller (in some places online, the author is listed as Linda Karen Miller, but I'm going to go by what it says on the cover of the book).
Populist Nationalism examines the political battlefield of the Progressive era and the early Republican Ascendancy period. In particular, the book follows the Republican faction leaders of the internationalists, reservationists, and irreconcilables during the debates on the League of Nations. However, a substantial portion of the book takes place after the election of Warren G. Harding, and can be used as a lens into the Harding years from the perspective of the legislative branch instead of the usual president-centered view that many authors take.
Foreign policy is the crux of the book, but each chapter takes the time to teach the reader many interesting aspects of domestic policy as well; foreign affairs do not exist in a vacuum, and the author certainly does not allow people to think that for a second. The work is scholarly and laser-focused on the maneuverings of what I took to be four main subjects: Sen. Hiram Johnson (R-CA), Sen. William Borah (R-ID), Sen. Henry Cabot Lodge (R-MA), and Secretary of State Charles Evans Hughes (R-NY). Borah and Johnson, the more progressive and populist of the four, are placed in a more protagonistic role from the framing of the book, but there is really no major bias toward any person described within. This allowed me as the reader to take many sides throughout the book without feeling that my positions were being critiqued by anyone other than the historical figures of the opposition movement; those who view the study of history as a dialogue between the past and present will be quite content.
If you are thinking of grabbing this book from the shelf, I must warn that it can be extremely dry at times due to its repetition of key points and the analytical feeling of the text toward politics. However, character traits are by no means absent from the book, and if you are prepared and in the market for a more serious read it will not be difficult to complete as it is not particularly long, just dense. I am glad to have read this so early into my studies of President Harding so that I can go into future research with a clear understanding of the motivations of varying Republican factions at the time. Since finishing Populist Nationalism, I have already noticed the ways that Harding as a presidential candidate panders to particular interests within his own party in order to achieve electoral unity between insurgent progressives and more moderate factions. One comes out of this read with the understanding that party disfunction was a specter that haunted nearly everything that the Republican Party core tried to do from 1911 through around 1924.