How many junior senators* have been elected president?
Three: John F. Kennedy, Warren Harding and … Barack Obama.
The first is regarded as great only by the underinformed (polls tend to rank him highly). Most people with some expertise regard Kennedy as merely pretty good (in Wikipedia’s summary of 16 historical rankings, Kennedy is never higher than the 86th percentile, or lower than the 62nd percentile).
And Harding? Pretty much always on everyone’s list of the worst presidents (Wikipedia lists 16 rankings that include both Harding and Nixon, and all but one has Harding rated lower … yikes … with 17th as the highest percentile).
Not sure if this evidence can tell us anything about Obama.
* The junior senator of a state is the one with less seniority.