Mitt is not helped by Newt’s attacks from the left. But Newt’s attacks from the right provide Mitt with an opportunity to not only try harder to sell himself to the conservative base of the GOP, but also subtextually suggest to mushy, unafilliated voters that Romney is not the extremist Democrats will try to portray should Mitt win the nomination. (Yes, that attack makes no sesnse to conservatives, but which GOP nominee has not been attacked as an extremist by the Dems?)
Moreover, regardless of what Newt does, Ron Paul is not going away. Paul will continue to amass delegates in hopes of influencing the platform and getting the most high-profile speaking slot he can negotiate at the convention. If Newt dropped out, the media narrative would inevitably devolve into a Romney-Paul discussion, likely funneling more votes and delegates to Paul. Should Romney win the nomination, it might be further useful to him to be accomodating “demands” from a second-place Newt on issues like Obamacare than having a media narrative of the GOP convention about struggles over defense cuts, drug legalization and the gold standard.
In short, Newt continuing his campaign may not be a “You know who this benefits?” situation… but it’s not clear that a Newtless campaign benefits Romney, either.