The biggest news to emerge after four weeks of parliamentary haggling over the naming of a new prime minister was the surprising transformation of Boris Berezovsky from an ardent supporter of President Boris Yeltsin into a dangerous adversary. Berezovsky is known for his uncanny ability to identify -- and cozy up to -- the prime source of political power, and his defection suggests he feels Yeltsin's days are numbered. The rift could widen quickly: For weeks Berezovsky has been expressing polite, muted concern about Yeltsin's health. Now he may start saying what he knows from years of intimate relations with Yeltsin's family and presidential chief of staff Valentin Yumashev. The next thing to watch for are leaks in the Berezovsky-controlled media -- which include Russia's biggest TV network -- questioning the President's ability to rule, based on deep concerns about Yeltsin's declining mental faculties.