Yes, I know Nixon was never formally charged, but he was pardoned by Ford. I still think that was technically incorrect. My suspicion is that an agreement was worked out whereby if Nixon resigned, Ford would pardon him so that Nixon could thus avoid prosecution. But it was procedurally wrong.
At this late date, I don't see Obama giving up the presidency for a pardon. His ego and arrogance won't allow it. He also knows that we have a number of spineless wimps in Washington who won't even try to prosecute him, lest they be perceived as racists.