What happened
Hillary Clinton and Barack Obama stepped up their attacks against each other as Tuesday’s Pennsylvania Democratic presidential primary approached. Obama said that Clinton changed her positions to suit the tastes of voters. Clinton said it was Obama—not she, as critics said—who was stooping to negative campaigning, including criticism of her health-care plan that she said amounted to an attack on universal health care. “That’s what Republicans do,” Clinton said. (Los Angeles Times, free registration) “Look, our campaign’s not perfect,” Obama said. “There’ve been times where, you know, if you get elbowed enough, eventually you start elbowing back.” (The New York Times, free registration)

What the commentators said
Obama’s staff accused Clinton of running a “100 percent negative” campaign, said Marc Ambinder in his blog at The Atlantic. Across Pennsylvania, half of Clinton’s paid ads have been negative—most of them focusing on Obama’s “bitter/cling” comments. The rest have been positive, so, as a point of fact, “they’re not running an entirely negative campaign.”

Obama has been denouncing “tit-for-tat politics” as he travels around Pennsylvania, said John Dickerson in Slate. But that takes “chutzpah,” given that while the candidate has been denouncing “distractions” his staff has been going to great lengths to maximize the damage from “Clinton's fantastical story about her breakneck race to shelter under sniper fire during a visit to Bosnia.”

The campaign sure has “spiraled deeper into the mud pit,” said Michael McAuliff in the New York Daily News. It started when Clinton “relentlessly” pounded Obama for saying that small-town Americans cling to guns and religion out of economic bitterness. It’s all fairly easy to understand, really. Obama had been rising in the polls in Pennsylvania, and Clinton needs a “blow-out” win there to keep her slim hopes alive.