is faking a divorce to remarry a us citizen ground for deportation?

He would first have to be charged and conficted with fraud or some other related offense and then authorities would have to decided whether to pursue revocation of citizenship.  Once citizenship is revoke, he could then be processed for removal.  Of course, the authorities would first need to learn about this before anything would happen.  Citizens cannot be deported, but if they obtained their citizenship unlawfully, it can be revoked and then they can be deported.