It's simple - if the bushies had his manuscript AND had his 2002 intelligence briefing and knew that the two were in conflict with each other but didn't inform Clarke of the same and allowed him to give that false information to the 9/11 Commitee, then they (the WH) suborned perjury, which is a crime in and of itself:
From the Dept of Justice Website
1752 Subornation of Perjury
To establish a case of subornation of perjury, a prosecutor must demonstrate that perjury was committed; that the defendant procured the perjury corruptly, knowing, believing or having reason to believe it to be false testimony; and that the defendant knew, believed or had reason to believe that the perjurer had knowledge of the falsity of his or her testimony.
To secure a conviction for subornation of perjury, the perjury sought must actually have been committed. United States v. Hairston, 46 F.3d 361, 376 (4th Cir.), cert. denied, 116 S.Ct. 124 (1995). The underlying perjury must be proved under the standards required by the applicable perjury statute. Thus, if section 1621 applies to the underlying perjury, the two witness rule must be met, but not if section 1623 applies to the underlying perjury. United States v. Gross, 511 F.2d 910, 915 (3d Cir.), cert. denied, 423 U.S. 924 (1975). Physical coercion need not be proven in prosecutions for subornation of perjury. United States v. Heater, 63 F.3d 311, 320 (4th Cir. 1995), cert. denied, 116 S.Ct. 796 (1996). Conspiracy to suborn perjury may be prosecuted irrespective of whether perjury has been committed. The two witness rule does not apply in conspiracy prosecutions. Solicitation of perjured testimony also may be prosecuted as obstruction of justice irrespective of whether the perjured testimony took place. United States v. Silverman, 745 F.2d 1386, 1395 (11th Cir. 1984).
Because the crime of subornation of perjury is distinct from that of perjury, the suborner and perjurer are not accomplices; however, a person who causes a false document to be introduced through an innocent witness can be held liable as a principal under 18 U.S.C. § 2(b). United States v. Walser, 3 F.3d 380, 388 (11th Cir. 1993).The attorney's ethical obligations when confronted by a client who wishes to testify falsely are discussed at length in Nix v. Whiteside, 475 U.S. 157 (1986).
See this DOJ document:
http://www.usdoj.gov/usao/eousa/foia_reading_room/usam/title9/crm01752.htm