“The effects of television advertising appear to last no more than a week — a ‘rapid decay,’ write the eggheads. A study of the 2000 presidential election finds the same decay. Campaigns may be wasting millions of dollars running ads weeks if not months before election day, only to have any effects of those ads dissipate. Case in point: the approximately $20 million that Bill Clinton spent in advertising between July 1995 and January 1996 — months before the 1996 election. The mastermind of this strategy, Dick Morris, wrote that ‘the key to Clinton’s victory was his early advertising.’ But there is little evidence that the ads mattered at all.” — John Sides rounds up the political science evidence on the effects of campaign advertising.