One of two things are going on...
Dclark is mafia – By saying whoever casts the third vote is going to be classified as mafia means he knows nobody is going to throw the third vote, so he thinks he’s safe.
Dclark is not mafia and extremely crazy, because if a townie doesn’t believe him and votes him out, the mafia wins when that person is lynched tomorrow.
What do I think? I think he knows the mafia wouldn't give themself up so easy if they were one of us. And a townie wouldn't want that suspicion on them so they won't vote him out if they don't believe him. Which means he's not expecting that third vote, so he's got no problem putting himself on the line and watching us whiff at eachother.
I think dclark is mafia.