Not really right now. I might be worried after he wins the general election by a semi-landslide. Not only because of some racists, but also because of some envious Republican lunatic who has forgotten to take his/her pills on November 4.
I doubt somebody would shoot Obama based on ideological/partisan reasons (unless it's a racist). The shooter would likely be a deranged lunatic or an anarchist.
IIRC Maxime Brunerie (if I remember his name) was a member of the MNR (Megret's far-right joke party) but tried to shoot Chirac only because he was deranged. IIRC he didn't claim to do it in the name of the MNR or any party.