Dubya wasn't left-handed.
But that's only because he wasn't a human being and wrote with the pen up his ninth arsehole.
Still, the proto thesis remains given that Cowboy Ronnie was a leftie.
Yer actual leftie Prezzes were:
20th James A. Garfield
31st Herbert Hoover
33rd Harry S. Truman
38th Gerald Ford
40th Ronald Reagan
41st George H.W. Bush
42nd William J. Clinton
44th Barack Obama