So Trump brought up perfectly valid issues, and many jumped on it. 

And Cruz got pretty far in the Republican race, despite being part Cuban. So i fail to see your point.

If Bush's team in fact did that, it was indeed disgusting tactics. But having a "love child" at all might have been more important to a conservative electorate than it being black. Otherwise, would not the fact he had adopted a Bangladeshi child be just as much of a turn-off?