There have been quite a few posts here about Henry A. Wallace becoming President, presumably if FDR had died by 1944 (or if FDR hadn't dumped him from the ticket that year--but the latter is unlikely, given the hostility to Wallace by urban bosses and Southern Democrats, and also given FDR's knowledge of the "guru letters"). However, I don't think anyone has explored the possibility that his father, Henry C. Wallace,
https://en.wikipedia.org/wiki/Henry_Cantwell_Wallace could have become President. (The premise for the following is of course that Henry C. Wallace does *not* die unexpectedly of complications following gall bladder surgery in 1924, as happened in OTL. Though he could have become president before then if an anarchist's bomb had exploded at a Cabinet meeting and killed Harding, Coolidge, and all the Cabinet members ahead of Wallace in the line of presidential succccession...)
Henry C. Wallace was editor of *Wallace's Farmer* and a leading figure in the organization of the Iowa Farm Bureau. He helped write the Republican farm plank in 1920, campaigned for Warren Harding among Midwestern farmers, and became Harding's Secretary of Agriculture in 1921. My thought was that Coolidge might worry in 1924 about La Follette making inroads among normally Republican farmers, and might therefore choose Wallace as his running mate. The Coolidge-Wallace ticket wins easily, but Coolidge is later assassinated by an anarchist (they *really* come in handy in these scenarios...) enraged over the Sacco-Vanzetti case, and Wallace becomes president.
However, a reading of Robert K. Murray's *The Harding Era* convinces me that this was unlikely. Wallace's relationship with Coolidge was anything but warm. Wallace may have been a leader of the conservative wing of the farmers' movement, but even that was too liberal for many businessmen who remembered his attacks on the packing and food-processing industries in *Wallace's Farmer.* And by 1923, under the influence of his son Henry A., he was becoming more sympathetic than previously to some sort of agricultural subsidies by the government. Harding was at least willing to listen to the idea, but Coolidge was not. According to Murray, "Wallace felt that Mellon and a big-business bias dominated the Coolidge administration as they had never done under Harding." (pp. 386-7)
So I would have to revise this: either (1) have someone other than Coolidge (and more sympathetic to Wallace) become Harding's running mate in 1920 and president in 1923; or (2) have Harding live and insist on choosing Wallace as his running mate in 1924, both because he liked him personally ("Hank," as Harding called Henry C., was a good golf and poker companion) and to win the farm vote. So Wallace gets on the ticket despite the Old Guard's grumbling. (And of course have Harding win re-election despite the scandals--given peace, prosperity, and the division in the opposition, I believe he could do so.) Harding dies after his re-election (he "suffered from high blood pressure and constant fatigue"
http://usnhistory.navylive.dodlive.mil/?p=32237 so if he didn't die in 1923, it's quite possible he would do so in a couple of years) and Henry C. Wallace becomes president. His administration is generally conservative, but he tries to get the federal government to take a more active role in agriculture, in cooperation with "farm bloc" leaders in Congress. And once he becomes president, the Republicans feel they have to re-nominate him in 1928, again despite misgivings by some conservatives. He would be elected easily.
No doubt Wallace would be unable to cope with the Depression, and would be voted out of power in 1932. Nevertheless, having him instead of Hoover as president could have significant effects. He would probably rely closely on the advice of his son Henry A. Wallace--and having been that closely associated with a recent and unsuccessful Republican *president* (not just a Secretary of Agriculture from the early 1920's), I wonder if Henry A. Wallace would be allowed the important role he had in OTL in the New Deal.