From CBS News' Dante Higgins:
ON THE ROAD IN N.H. – While traveling with John McCain on the Straight Talk Express today, word of a new Mitt Romney ad criticizing McCain made it around the bus.
The news sparked a long conversation on immigration with the press aboard the bus and McCain even summoned advisor Charlie Black to the back of the bus to discuss the news.
Earlier today in Dover, McCain told reporters that he had already responded in his own ad released last night and now he's done with it.
"It's time to move on. We're going to run this campaign in a positive fashion. We have to respond to attacks which we have had and we're moving on," McCain sais.
"We're running for president, not against Governor Romney, but for the votes of the people of New Hampshire ... I think the people of New Hampshire are very sophisticated and will see right through these attacks. He's made other attacks on other people who he has seen as moving up in the polls, so I view it in some ways as a form of flattery. And it's also hard to respond sometimes because the position he has today may not be the position he has tomorrow."