There is absolutely no way whatsoever that Obama would endorse Clinton before the nomination has been locked up- you don't treat your Vice President that way.
Unless you're Eisenhower.
During the 1960 Presidential election, a reporter asked Eisenhower if he could give an example of a major idea of Nixon's that he had heeded. Eisenhower responded with the flip comment, "If you give me a week, I might think of one." (Wiki)
This was more a joke. Ike did not want JFK as his sucessor. Both men disliked each other.
