He did very well in the first debate and then decided to coast in from there rather than risk a more aggressive tone in the last two debates and in the last months of the campaign in general.
Not accusing you of anything but isn't it a sad statement on our society when the advice for Romney is he should have gotten more aggressive (i.e. nasty as did Obama)
Or Romney just calculated, getting nasty would have blown back on him, as it did the few times he tried it (Benghazi, embracing Birtherism, etc.)
Of course, what you call, "getting nasty", I call actually challenging his position.
His position was he was a turnaround artist. He understood business.
Pointing out the AmPads and the GS Steels and the KB Toys and other companies where Bain totally fucked over people to make a profit wasn't "getting nasty", it was pointing out the human cost of his kind of economics.