Barack Obama's Tuesday losses were like splash of cold water on a campaign too comfortable with its recent dominance. But is the problem now going to be one of the campaigns becoming too aggressive? Yesterday, in an ominous sign, Obama adviser Samantha Power called Hillary Clinton a "monster" (read our take on that). But while that smear was immediately condemned by Obama, his political team clearly believes that he has to be more aggressive, especially in the face of stepped-up Clinton attacks that include comparing Obama to, yes, Ken Starr. Many commentators are already warning Obama to be careful as he wades into the muck.

• David Brooks writes that by fighting fire with fire, Obama would betray his campaign's core beliefs. [NYT]

• Andrew Sullivan thinks Obama has to stay positive while letting his surrogates go negative, a role for which he happily volunteers. [Atlantic]

• Victor Davis Hansen suggests that, instead of going negative, the Obama campaign might simply try to run out the clock and secure a win with its delegate lead and a continued message of hope. [Corner/National Review]

• Kevin Drum is worried about all the material Obama and Clinton are giving to McCain, but also wonders whether intra-party primary smears are ever used in the general election. [Political Animal/Washington Monthly]

• Mark Halperin lays out ten reasons that going negative could be politically dangerous for Obama. Number seven: It could free up Clinton to attack him even more. [Page/Time]

• John Dickerson says Obama's situation is nothing new, except that now with the general election near, he has to show how he'll respond to attacks using his unique political gifts. [Slate]

• Steve Almond suggests that Obama continue to take the high road and kill Clinton with kindness. [HuffPo]

• Jill Lawrence writes that the superdelegates' general opposition to negativity will keep both campaigns in check. [USAT] —Dan Amira

For a complete guide to presidential candidates Hillary Clinton, Barack Obama, and John McCain — from First Love to Most Embarrassing Gaffe — read the 2008 Electopedia.