A Democratic presidential candidate, John Edwards, is averting a politically damaging clash with liberal bloggers by rejecting a call to fire two campaign staffers who used vulgar and allegedly anti-religious language in recent blog posts. Left-leaning online activists had bluntly threatened to abandon Mr. Edwards’s campaign for the Democratic nomination if he acceded to the demand from the Catholic League to dismiss the two Web-savvy women, Amanda Marcotte and Melissa McEwan.