Would Theodore Roosevelt have become a Democrat at some point?

[All Along The Watchtower]

I think he'd at least by sympathetic to the New Deal, after all it was modelled after his Square Deal, but whether he'd vote for FDR would depend on familiar tensions.

There weren't any between Franklin and TR. TR ADORED him and said to him once that if he could have had one wish it's that "you would've been a Republican".

Yeah, the one who hated FDR was TR's daughter, Alice Roosevelt Longworth, who was a fascinating and idiosyncratic woman not all of whose views reflected her father's.

Don’t forget his ultra-right-wing son Archibald.

[All Along The Watchtower]

Anyway, I don’t think TR would have had much of a problem with any subsequent Republican presidential nominee tbh—other than, of course, the major issue that they were not him.

To paraphrase another Republican President from New York who didn’t believe in term limits and who certainly used the “bully pulpit”, if in the crassest and most obnoxious schoolyard sense of the first word in that term, TR tended to believed that he alone could fix things. In this, he was much like four-term-holding fifth cousin.