Gallup's latest numbers somewhat minimize one of his strongest arguments. In two-way match-ups, Romney's lead over Obama is well within the margin of error, and Obama's lead over Cain is the same. Even with Perry, Obama's lead is only 5 points, just outside the margin. If Cain can show he has as much general election appeal as Romney, then one of Mitt's key primary arguments evaporates.
The other factor the poll brings to the fore is the enthusiasm gap. Republican hostility to Obama currently outpaces Democratic excitement in the election. Which is why, I suspect, some truly nasty, populist negative ads will be unleashed to damage Mitt if he gets the nod. And not from the Obama campaign directly.