@Ubik
1988 convention data from 538.
POLLING AVERAGE
YEAR HEADING INTO CONVENTIONS 30 DAYS AFTER CONVENTIONS ACTUAL RESULT
1972 Nixon +16.0 Nixon +29.7 Nixon +23.2
1976 Carter +13.0 Carter +4.0 Carter +2.0
1980 Reagan +6.0 Reagan +2.6 Reagan +9.7
1984 Reagan +14.3 Reagan +16.8 Reagan +18.2
1988 Dukakis +6.7 Bush +3.0 Bush +7.7
1992 Bush **.0 Clinton +11.7 Clinton +5.6
1996 Clinton +16.8 Clinton +16.0 Clinton +8.5
2000 Bush +4.3 Gore +2.0 Gore +0.5
2004 Kerry +2.7 Bush **.8 Bush +2.5
2008 Obama +3.8 Obama +3.1 Obama +7.3
2012 Obama +2.3 Obama **.9 Obama +3.9