More ammunition for Barack Obama in this morning's USA Today:

LITTLE ROCK - Federal archivists at the Clinton Presidential Library are blocking the release of hundreds of pages of White House papers on pardons that the former president approved, including clemency for fugitive commodities trader Marc Rich.

That archivists' decision, based on guidance provided by Bill Clinton that restricts the disclosure of advice he received from aides, prevents public scrutiny of documents that would shed light on how he decided which pardons to approve from among hundreds of requests.

Clinton's legal agent declined the option of reviewing and releasing the documents that were withheld, said the archivists, who work for the federal government, not the Clintons.

Clinton's decision to go negative, coupled with Obama's resolve to fight back ensures this race is going to stay ugly. Samantha Power's remarks (and subsequent apology) are yet another indication of how personal the animosity between the two camps has gotten, and how dug in each side's supporters are.

As to the battle itself, everyone has an opinion:

David Brooks argues Obama is in danger of being stripped down to a run of the mill politician by the fight.

Jon Chait calls Hillary's strategy "pretty repulsive."

Matt Cooper says Obama needs to dispense with "math" talk and stop whining about the press.

Visit the RCP home page for much more.