The authors examine the dynamics of public opinion formation and change around a sitting president and their implications for reelection contests. Because of the biases inherent in information processing and the information environment, two distinct, but simultaneous, effects of citizen learning during a presidential term are expected. For those with prior opinions of the president, learning contributes to more polarized evaluations of the president. For those initially uncertain about the president, learning contributes to opinion formation about the president. Because the gap in uncertainty generally favors the incumbent over a lesser-known challenger, races with an incumbent presidential candidate are typically marked, perhaps paradoxically, by both a polarization of public opinion and an incumbency advantage.