According to what we know, Romney’s campaign did not offer to make a public apology — the campaign said he would say x about Rush “if he was asked about it.” As Mark Twain said, “A lie can travel halfway around the world while the truth is putting on its shoes.” If Romney were sincere about correcting a serious mis-statement that he made, he would have promptly issued another statement — not called Rush and offer to correct it “if asked.”
And I personally hold Romney accountable for the statements his own campaign issues to the Huffington Post (as I hold all candidates responsible for statements their campaigns issue). The only other option is to believe that Romney has a very serious campaign management problem to allow his spokesperson to send out unvetted statements on breaking issues.