Here's why Obama stopped the race card

In the Michigan Primay

Though Obama carried the young and black vote, Clinton received 56% versus "uncommitted" and Kucinich:

The results show Clinton's strength

Clinton was the only top-tier presidential candidate on the ballot in the Democratic primary, and she carried 58 percent of the overall vote, while 37 percent of the voters in the Democratic primary chose to vote uncommitted.

According to the exit polls

If all candidates were on the ballot:

clinton 46
obam 35
edwards 12