From FactCheck.org:
McCain was asked by a New Orleans reporter why he voted twice against an independent commission to investigate the government’s failings before and after Hurricane Katrina, and he incorrectly stated that he had "voted for every investigation."
McCain actually voted twice, in 2005 and 2006, to defeat a Democratic amendment that would have set up an independent commission along the lines of the 9/11 Commission. At the time of the second vote, members of both parties were complaining that the White House was refusing requests by Senate investigators for information.
The McCain campaign accused the Obama campaign of "tired negative attacks" for pointing out and documenting McCain’s gaffe.
So in fact, McCain defended George Bush at the expense of the American people. Even McCain's best buddy Joe Lieberman said the White House was playing games and we should support this commission.
The other co-chair of that Senate investigation, Democratic Sen. Joe Lieberman of Connecticut, more forcefully chastised the White House and other federal agencies for withholding documents, refusing interviews and derailing the Senate's work.Lieberman, Jan. 24, 2006: There has been a near-total lack of cooperation that has made it impossible, in my opinion, for us to do the thorough investigation we have a responsibility to do.