BARTLET'S OVERSIGHT ABOUT HIS MEDICAL CONDITION COULD CRUSH HIS PRESIDENCY; OLIVER PLATT GUEST STARS - The President's vaunted administration could be brought down by the tiniest oversight as Bartlet secretly summons chief counsel Barash (guest star Oliver Platt, "Bulworth") to discuss how his failure to divulge his multiple sclerosis condition could be a criminal violation of full disclosure -- which would give his enemies enough ammo to destroy him. Meanwhile: a fuming Toby orders C.J. to smoke out the insider who leaked vital information on the President's reversal on school vouchers; Sam feels queasy when he learns that an aging oil tanker is leaking onto the coast of Delaware causing an ecological disaster -- and he could be liable since he brokered the deal for the behemoth in his previous shipping firm job while aware of the needed repairs; Josh clashes with a questioning Donna as the U.S. prepares a big cash loan to prop up the collapsing Mexican economy again.