Saying that he is is self-destructive and it works against us.
There is a Latin saying, falsus in unum, falsus in omnibus ("false in one thing, false in all"). It means that if we falsely accuse Obama of being a Muslim, his defenders can point to that and say it reflects on everything we say about him, even if it's true. The National "Jewish" Democratic Council is pointing to this accusation to show that Obama's detractors are evil, dishonest, running a smear campaign, and so on. NJDC is actually a weak point in the opposing side's lines and it it is a good thing to attack politically, but not with weak and unsubstantiated arguments.
Instead, let's just tell the truth about Obama:
(1) Obama is not a Muslim. He is a member of a nominally Christian church with a racist and Israel-hating pastor. (We have not seen Jeremiah Wright say anything explicitly about "Jews," so we won't call him an anti-Semite.)
(2) Obama consorts openly with the prominent racist and anti-Semite Al Sharpton and his National Action Network. We should circulate pictures of this, along with the things Sharpton and his entourage have to say about Jews and white people in general.
(3) Obama solicited and accepted support from MoveOn.org, an arguably anti-Semitic and anti-Catholic hate organization. This needs to be circulated in NY and PA, where we have a lot of Irish, Polish, and Italian Catholics. Show them MoveOn's photomanipulation of Pope Benedict waving a gavel in front of the U.S. Supreme Court.
As stated by Aesop, birds of a feather flock together. If Obama doesn't want us to take him for an anti-Semite (and racist), he should not surround himself with anti-Semites and racists.
(4) Obama also supports live birth abortion (infanticide) as shown by his opposition to Illinois Born Alive Infants Protection Act. Even the pro-choice side isn't going to stand on that hill with him, and he can kiss Pennsylvania and possibly New York goodbye; there are strong pro-life movements here, and we need to involve them.