I assume he loses, since he was extraordinarily unpopular at the end of his term, but how bad? Worse than the OTL landslide or is the power of the incumbency (even a really unpopular incumbent) enough to make it a little closer? Could he conceivably be denied the Democratic nomination? I know he lost the New Hampshire primary to Kefauver before he officially announced he wasn't running, but primaries were less important back then and I'm sure a sitting President could have corralled enough party bosses to secure the nomination if he really wanted it. Would there be any longer term impact of Truman running in 1952 or would it just be an interesting footnote that doesn't change much?