Mitt Romney is fond of doing the worst kind of political attack. That is one that is easily defended against, and in many cases disproven. An example of this is the "Obama wants to gut welfare attack, unlike Bill Clinton". The memo Obama issued clearly states that any waiver can't lower the work requirement, and furthermore the exalted Democrat whom Romney refers to is alive and supporting Obama. These kind of attacks ultimately make you look desperate to informed voters.
The opposite of this should be on the Democrat's hit list:
During his acceptance speech at the RNC, Romney failed to thank troops and talk about his policy vision for the current war.
This is the best kind of political attack because it can't be undone. There is no valid excuse that would render the attack moot.
There's nothing Romney can do to make it less relevant. For the rest of the campaign he'll never have as big an audience with 100% total control over the message. He simply messed up.
An apology would fall flat because it reminds people that you did it in the first place (see Todd Akin). Could you imagine Romney giving a speech at the RNC and not talk about Obama? about taxes? his family? etc.
This is perfect for outside groups, especially veterans who support the President to make a tough ad and play it over and over for the next 56 days.