"Under Newt Gingrich earmarks doubled. Rick Santorum was a major earmarker and continues to defend earmarks. Under Rick Santorum he voted to raise the debt ceiling I believe five different times to a tune of about an additional $3.5 trillion," Romney said. "I believe that while Sen. Santorum was serving in Congress and the Senate, government spending increased by some 80 percent. Republicans spent too much money, borrowed too much money, earmarked too much, and Rick Santorum and Newt Gingrich have to be held accountable."

He went on to accuse his pair of rivals of "acting like Democrats."

"When Republicans act like Democrats, they lose. And in Newt Gingrich’s case he had to resign. In Rick Santorum’s case, he lost by the biggest margin of any Senate incumbent since 1980. Borrowing, spending and earmarking is not a good combination if you’re a Republican and not a good combination, in my view, for America," Romney said.

Romney hopes that by pairing Gingrich and Santorum together, he can associate the former Pennsylvania senator with Gingrich, into whom Romney's campaign and its allies have invested substantial time and effort criticizing throughout the primary process. Gingrich has credited Romney's attack ads for undermining his once-surging campaign, but Santorum has emerged from the early-voting states relatively unscathed — ikely part of the reason he was able to pull of surprise victories in Minnesota, Missouri and Colorado.

Earlier Wednesday, Romney strategist Eric Fehrnstrom described Gingrich and Santorum as "two peas in a pod" during an interview with MSNBC.

Romney also downplayed the results of Tuesday night's vote, arguing his campaign had not been fully engaged in the contests, which did not carry pledged delegates.

“We think we can beat Sen. Santorum where we compete head-to-head in an aggressive way, and we obviously didn’t do that in Colorado or Minnesota to the extent that the other campaign did," Romney said.

Romney also insisted that he expected — and was prepared for — a prolonged battle for the Republican nomination. Fehrnstrom suggested earlier in the day that his campaign didn't anticipate a clear victor emerging until “late spring, probably April or May.”

"There's no such thing as coronations in presidential politics," Romney said. "It's meant to be a long process. It's not easy to get the nomination. It's not easy to be elected president."