Some of the harshest words are coming from 2008 presidential hopefuls. Sen. Hillary Rodham Clinton of New York ridiculed relief coordinator Michael Brown's suggestions. Former North Carolina Sen. John Edwards said the hurricane's aftermath underscores the "two Americas" theme of his presidential campaign last year.
"It's piling on time," said Rutgers University political scientist Ross Baker.
Democrats, ready with talking points and working closely, went into full battle mode Wednesday.
Clinton sought an independent commission to study the response and made the rounds of four network morning television shows, taking on Brown, director of the Federal Emergency Management Agency.
"I would never have appointed such a person. I would imagine, I don't think that anybody would. You would appoint somebody who has experience," Clinton told CBS News.
Brown spoke with CBS' Harry Smith on The Early Show.
"Did you screw this up?" Smith asked.
"No. No," Brown said.
Senate Democratic leader Harry Reid of Nevada pressed for a broad investigation that would explore questions such as "How much time did the president spend dealing with this emerging crisis while he was on vacation?"
His House counterpart, Rep. Nancy Pelosi, D-Calif., renewed her call for Brown's dismissal. "There were two disasters last week: first, the natural disaster, and second, the man-made disaster, the disaster made by mistakes made by FEMA," she said.
CBS News Correspondent Gloria Borger reports
"Why would I do that?" Pelosi quoted the president as saying.
White House counselor Dan Bartlett challenged Pelosi's account as "inaccurate and unfortunate."
As a party, Democrats had spoken with different voices on Iraq. Some Democrats — including Clinton, Edwards and 2004 presidential nominee Sen. John Kerry of Massachusetts — had voted to support the Iraq war resolution in October 2002.
Many Democrats were careful in their criticism of Mr. Bush's handling of Iraq so as not to appear to undermine U.S. troops or encourage the insurgency.
Democrats also were reluctant to criticize the president as the nation rallied behind him after the attacks of Sept. 11, 2001.
Such caution, however, is not a factor in the open season on Mr. Bush's handling of the hurricane.
"It is different when you face a foreign enemy on the one hand versus a domestic failure on the other," Democratic consultant Mark Mellman said.
"Democrats see a real problem with the way this administration has handled Katrina, and see real needs that have to be addressed. Everybody is trying to do the best they can to help these victims," Mellman said.