by Peter Suderman 

Richard Johnston and Emily Thorson analyze polling data from the 2008 election and find a close link between declines in support for John McCain and declines in approval for -- who else? -- Sarah Palin:

John McCain’s August 29 announcement of Palin as his running mate surprised the Republican establishment, the media, and especially voters. She made a strong first impression: she enjoyed high approval ratings after her acceptance speech, and the percentage of voters saying that they intended to vote Republican skyrocketed. But within days of the speech, her ratings began a precipitous slide from which sheand the McCain campaignnever recovered. Throughout the rest of the campaign, vote intentions were closely tied to Palin’s approval ratings: each major Palin approval drop was followed, within a day or two, by a drop in McCain vote intention. No other factor moved McCain support with such precision. 

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