5 reasons why the Governor Bill Richardson endorsement of Obama was just what the doctor ordered:

1. Timing. Two words: Reverend Wright.
2. Superdelegates.   Richardson is one. This sends a message to other superdelegates.
3. Richardson is close to both Clintons. "[S]ymbolically his connections with the Clintons will raise questions as to why he decided to turn his back on the New York senator, rather than remaining neutral in the nomination battle."
4. Experience. Richardson has it. If Obama can be "guilty by his association" with Rev Wright, then he can be experienced by his association with Richardson, who has an extensive foreign relations resume.
5. Hispanics. "Clinton still will be heavily favored to win the Puerto Rico primary in June, but as the first Hispanic candidate for president, Richardson's endorsement speaks to a weakness in Obama's candidacy."

This, or any, one endorsement isn't exactly like waving a magic wand over Obama's candidacy. But:

Richardson's endorsement and in particular his warning about the consequences of indefinite conflict may influence other Democrats still trying to decide what to do.