This paper examines the potential for attrition bias and panel conditioning in a longitudinal online election panel survey. The 2008 Associated Press-Yahoo! News Poll was conducted by Knowledge Networks with contributions from political scientists at Harvard University and Stanford University. The study involved an eleven-wave Web panel election survey of general population U.S. adults. All the interviews were conducted with KnowledgePanel® respondents. Our assessment of panel conditioning is made possible by the study’s sample design, which includes both the longitudinal sample component as well as three separate fresh cross-sectional samples. We examined the potential for the impact of panel conditioning on self-reports of certain attitudes, preferences, and behaviors such as the propensity to remain undecided and to report being certain about voting or having voted early. We employ Extended Cox hazard modeling to estimate risk factors responsible for attrition from the panel study. We found some evidence of panel conditioning for one political knowledge question. Not surprisingly, longitudinal respondents were more likely to correctly name Obama’s religion than cross-sectional respondents, confirming previous results from the literature for panel conditioning on knowledge questions. For the other seven items about the presidential election, only two showed some evidence of panel conditioning. Regarding panel attrition, the rare (i.e., non-whites, adults ages 18 to 29, or less than high school education) and non-rare respondent groups were attriting from the panel at the same rate during the first four waves, probably due to a specific incentive system put in place for the rare respondents. Undecided Republicans were more likely to quit the panel during the first four waves than Republicans who chose John McCain. In subsequent waves, late-participating respondents were more likely to drop from the study than early respondents in both rare and non-rare groups.