I agree they are holding out for the convention and post convention, and likely have an effective plan to knock Obama out for good. I do not agree with the above sentence. While they have not handled all these attacks perfectly (See the ridiculous statement from Andrea Saul yesterday for a perfect example), Obama is not winning anything. He is mired below 45%, which seems to be a position they cannot get out of, no matter how much money they spend this summer. Seeing a campaign spend as they have this summer is highly unusual, and they have done little to nothing to bolster their candidate's position. They have hit Romney hard, but if it was having any real impact, you can be damn sure the Romney campaign would do something larger to counter it. Instead, Romney has been investing the time hitting the swing states and focusing on strengthening his position as the much better option to get the economy going. He remains well ahead in that metric, which is what people are voting on. They have enough money in the bank, as do the PACs, that if Romney was in bad shape, they'd start spending some cash.
Of course, Obama could still be blowing through "primary" cash, which can't be carried forward to the general election, IIRC.
Unlike McCain, or Bob Dole, who were running "Because it was their turn", Romney wants this job. I think that he will do what it takes to get it.