Could be? I suppose he is right. For a sin to be a mortal sin it must be an inherently grave evil—yes, voting for a pro-abortion candidate is inherently gravely evil. The person must know it is inherently gravely evil and must freely elect to do so. Clearly those who voted for Obama meet the last criterion. Unfortunately, they may be as stupid as squid in that they do not realize that abortion and voting for a pro-abortion candidate are inherently gravely evil. Unfortunately, too few bishops and priests have given sermons on these evils.
In the words of George Carlin, you’ve “gotta wanna” commit mortal sin.