Let us just take One (1) year, and some samples.
Romney for Obama in 2011
White House Quotes Romney in Defense of Health Care
Mitt Romney Sends Leftover Pizza to Obama Chicago HQ After spending the day in Chicago fundraising, Mitt Romney sat down with small business owners at Gino's East, a pizza joint famous for their deep-dish pizza. In fact, Romney himself tweeted a photo of a delivery boy heading out with the loot, writing, "Great deep dish at @ginoseast. Sending the extra slices to @barackobama and his Chicago HQ team."
Romney - the One and the Only "Magic RINO(TM)":
"Obama was born in the United States"
"Obama Doesnt Need a Birth Certificate"
"The citizenship test has been passed"