You can see McArthur's initial campaign kickoff announcement for Martin here:
And here's the video where McArthur uses the racial slur "raghead" (start watching at about 1:30, he uses the term around 1:43):
Of course, Dana Loesch happily promoted the speech:
Update: Fixed spelling of McArthur. Also, this post was linked to on the Post-Dispatch's Political Fix blog. Check the comments there if you'd like to see some wingnuts attempting to justify racial slurs. Fired Up! Missouri also linked here. Readers directed here by Dana Loesch should see this post.