The Bush administration says some key White House officials and documents are off-limits to congressional investigations into the failures of the Katrina disaster.
Democrats, like Connecticut Sen. Joe Lieberman, are fuming.
Lieberman is the ranking Democrat on the Senate Homeland Security and Governmental Affairs Committee, which is conducting the investigation.
"A lot of federal government employees who we've interviewed, they've been told by the White House that they can't answer any questions about communications they had with people at the White House," Lieberman told ABC News. "Now, that's stonewalling. For the administration to simply tell people in the federal government they can't talk to our investigators about any of the conversations they had with people at the White House is unacceptable."
The White House said it is cooperating, providing Congress thousands of pages of documents and making more than 120 officials available. But it said some of the president's closest aides must be able to freely offer advice without fear their positions will be made public.
"Now, the issue you bring up goes to separation of powers issues," said White House press secretary Scott McClellan during a White House briefing. "The president believes that Senator Lieberman ought to have the right to confidential conversations with his advisers just like all presidents have asserted they ought to have that same right. That's what this is about. That's the bottom line here. "
A separation of powers showdown appears to be brewing, with Lieberman threatening to pursue subpoenas to force the White House to comply.
The White House could invoke executive privilege, a legal position often upheld in the courts.
Beware the Public Debate
But Lanny Davis, the former White House counsel for the often-embattled Clinton administration, said the public's right to know may trump a strong legal argument.
"I can remember a dozen times or more where Congress served the Clinton White House with subpoenas for documents where we had every constitutional right to say no, and we did, and we fought, and we delayed, and we were accused of cover-up, and we gave in," Davis said.
White House critics plan to use the president's own words against him. They point to his national address in New Orleans in the days after Katrina.
"The United States Congress also has an important oversight function to perform," said Bush during a televised address from New Orleans' Jackson Square. "Congress is preparing an investigation, and I will work with members of both parties to make sure this effort is thorough."
But some complain that pledge of cooperation apparently only goes so far -- at least for now.
ABC News' Pierre Thomas filed this report.