Evan Vucci, Associated Press
Republican presidential candidate, former House Speaker Newt Gingrich looks on during a church service at St. Ambrose Cathedral on Sunday, Jan. 1, 2012 in Des Moines, Iowa.

DES MOINES, Iowa — Newt Gingrich said Sunday his GOP rival Mitt Romney would buy the presidency if he could.

Speaking to reporters after attending Mass at the St. Ambrose Cathedral in Des Moines, Gingrich said the amount that the former Massachusetts governor will eventually spend on his various campaigns will rival the spending of billionaire New York City Mayor Michael Bloomberg.

"Romney would buy the election if he could," Gingrich said.

A political action committee supporting Romney has rolled out ads attacking Gingrich in the days before Tuesday's caucuses. They have helped erode his support in the state.

A new Des Moines Register poll put Gingrich in fourth place, after leading the field a few weeks ago.

The former House speaker said Sunday that the most accurate part of the survey was that 41 percent said they could change their opinion.

"And I think that's an understatement," he said. "I think this is wide open and that the next 2 ½ days are going to be fascinating."

The former House speaker is set to make three campaign stops later Sunday in Iowa.