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I stated just a second ago that the conventional wisdom that undecideds break for the challenger does not hold true at the Presidential level.

Here is some evidence to back my assertion up. I'm using Gallup here, since they have available data going back over many elections. In each case, I am presenting the results from a month before the election, the results in the poll before the last one (their last one never has undecideds), and the election results.

Year	Race	1 Month Out	Next To Last Poll	Result	Verdict
1936	Incumbent FDR vs. Landon	FDR 51, Landon 44	FDR 54, Landon 43	FDR 61, Landon 37	Broke towards incumbent
1940	Incumbent FDR vs. Willkie	FDR 51, Willkie 42	FDR 51, Willkie 42	FDR 55, Willkie 45	Broke evenly
1944	Incumbent FDR vs. Dewey	FDR 47, Dewey 45	FDR 47, Dewey 45	FDR 53, Dewey 46	Broke towards incumbent
1948	No incumbent pres, incumbent VP Truman vs Dewey	Dewey 46, Truman 40	Dewey 50, Truman 45	Truman 50, Dewey 45	Broke towards the incumbent VP
1952	No incumbents. Dems incumbent party. Ike vs. Stevenson	Ike 51, Stevenson 38	Ike 48, Stevenson 39	Ike 55, Stevenson 44	Broke evenly
1956	Incumbent Ike vs Stevenson	Ike 51, Stevenson 41	Ike 51, Stevenson 41	Ike 57, Stevenson 42	Broke towards incumbent
1960	No incumbent pres. Incumbent VP vs Kennedy	Kennedy 49, Nixon 45	Kennedy 49, Nixon 45	Kennedy 50, Nixon 50	Broke for incumbent VP
1964	Incumbent LBJ vs. Goldwater	LBJ 64, Goldwater 29	LBJ 64, Goldwater 29	LBJ 61, Goldwater 38	Broke towards challenger
1968	No incumbents. Dems incumbent party. Humphrey vs Nixon	Nixon 43, Humphrey 31	Nixon 44, Humphrey 36	Nixon 43, Humphrey 43	Broke towards incumbent party
1972	Incumbent Nixon vs McGovern	Nixon 60, McGovern 34	Nixon 59, McGovern 36	Nixon 61, McGovern 38	Broke evenly
1976	Incumbent Ford vs Carter	Carter 47, Ford 41	Carter 48, Ford 44	Carter 50, Ford 48	Slight break towards incumbent
1980	Incumbent Carter vs Reagan	Carter 47, Reagan 39	Carter 47, Reagan 39	Reagan 51, Carter 41	Broke strongly towards challenger. So did some of the decideds.
1984	Incumbent Reagan vs Mondale	Reagan 58, Mondale 38	Reagan 56, Mondale 39	Reagan 59, Mondale 41	Broke evenly
1988	No incumbent pres. Incumbent VP Bush vs Dukakis	Bush 49, Dukakis 43	Bush 53, Dukakis 39	Bush 53, Dukakis 46	Depends on which you use. Broke evenly from a month out. Broke slightly towards challenger from the 2nd to last.
1992	Incumbent Bush vs Clinton	Clinton 47, Bush 29	Clinton 43, Bush 36	Clinton 43, Bush 38	Broke towards incumbent
1996	Incumbent Clinton vs Dole	Clinton 48, Dole 39	Clinton 52, Dole 41	Clinton 49, Dole 41	Broke evenly
2000	No incumbent pres. Incumbent VP Gore vs Bush	Bush 48, Gore 43	Bush 47, Gore 45	Gore 48, Bush 48	Broke towards incumbent VP

Hey, that's really interesting! I'm gonna have to revise my approach now so I'm unsure how I would speculatively distribute the EVs except to say that I would assign Kerry notably less than I had previously. Almost certainly no more than 295, off the top of my head.

Thanks for posting that!

"1948: No incumbent pres, incumbent VP Truman vs Dewey"

One nit: Truman was the incumbent president in 1948, since FDR died in 1945. While Truman had not been elected president, neither had LBJ when you correctly referred to him as the incumbent president in 1964 (nor Ford in 1976).

Thanks for posting that.