This article examines the situations under which candidates in multicandidate races go on the attack (both intraparty and interparty), paying special attention to the timing of the attacks, whether the attacker or the attacked is a front-runner or trailing, and candidate ideology. Using ad tracking data from the 2004 and 2008 U.S. presidential nomination campaigns and detailed polling data from each state, the authors find that timing is an important consideration in launching an attack and that candidate ideology determines who gets attacked. While candidate standing and candidate resources have little influence on intraparty attack behavior, both are important predictors of attacks across party lines.