I think this is a bit too low frequency to qualify as "dog whistle":
[Grover] Norquist dropped by The Times’ Washington bureau today and, as part of his negative critique of Obama’s liberal stances on economic issues and other matters, he termed the presumptive Democratic presidential nominee "John Kerry with a tan."
Earlier this year, the RNC did polling to determine how far they could go in their attacks before they would be perceived as "racist." Not, one would imagine, because they really cared — but rather, as John Judis noted in an interesting article in TNR, because "too far" could backlash.
He brings Princeton political scientist Tali Mendelberg’s analysis of the Willie Horton ad in her book, The Race Card:
Mendelberg’s most controversial claim is that these ads work best when the appeal is implicit. If the appeal is explicit, she argues–that is, if politicians actually say that blacks are undeserving–then they lose support because they have violated the norm against racism. Although voters will respond unconsciously to an implicit appeal that they don’t perceive as racist, they will recoil for reasons of conscience or social disapproval to an appeal that either is, or is seen as, racist. Mendelberg asserts that Bush actually lost support to Dukakis in the closing weeks of the 1988 campaign because, on October 21, Jesse Jackson denounced the Horton ad as racist and Dukakis’s running mate Lloyd Bentsen followed suit two days later. That made explicit what had previously been implicit.
Despite all their polling, it just doesn’t seem like the Republicans are going to be able to keep themselves from hurtling over that line into "explicit" territory.
Or maybe Grover just didn’t get the memo.