It seems like the untrustworthy Newt is the one that should drop out and stop splitting the vote.
Newt is by far the best attack dog in the field. He needs to stay in and destroy Romney for a conservative to have hope of winning the nomination.
Newt is politically astute enough to realize that his attacks may not personally benefit him. In fact it could draw down his support while undermining Romney's support. The beneficiaries could be Santorum and/or Perry. Negative campaigning is a risky strategy when there are more than just two options. However, Newt is likely to do it anyway because he is so disgusted with Romney.