Enthusiastic as one might be that Jack Lemmon has found a new lease on movie life with his Grumpy Old Men series, the funny-crankpots genre wears mighty thin on this road trip. In My Fellow Republicans, Lemmon plays a frugal, Bush-type Republican ex-president, James Garner (grumpy old Maverick guy) a skirt-chasing Clinton-type Democratic ex-president, and the two find themselves on the run from a scandal that may have been stirred up by Dan Aykroyd (grumpy, middle-aged Ghostbusters guy), the sitting commander-in-chief. Some of the grumpiest lines from one ex to another: ”You’re a whore, admit it.” ”Screw you.” ”Who am I, f—-n’ MacGyver?” (Actually, that one is funny.) The supporting cast is promising — John Heard as a Dan Quayle-style Vice President, Sela Ward, Marg Helgenberger, even grumpy old Lauren Bacall — but the antics (jokes about the Japanese, penis names, gay Secret Service agents, and the lyrics to ”Hail to the Chief”) are about as tired as a stack of position papers on election finance reform. Eventually Lemmon and Garner run down their engines and are left looking like a couple of nice old actors stranded by their campaign managers.