The President has not taken force off the table and he has also said that Iran must not get a bomb. The question is whether anyone actually believes that. What Romney said was, "“This is a president who has failed … to communicate that military options are on the table and in fact in our hand”
Saying something doesn’t necessarily communicate it if no one believes it, and a lot of people, both the President’s opponent, and his supporters, don’t believe he’d ever attack Iran, no matter what.
Personally, I think he’d blow up the whole country without a second thought, wimpiness in the face of foreign threats is not one of his weaknesses as President. But I don’t think it’s dishonest for people to have a different view.
The President says a lot of things. One of his actual weaknesses is that he doesn’t always do what he says he’ll do. As one of his spokesman said after a speech he gave on health care, “The President’s statement was not meant to be taken literally.”