Romney tries to stunt Santorum

Sensing a possible threat, Mitt Romney criticized Rick Santorum's time in the Senate as "not effective" because of his past support for spending on pork-barrel projects as he worked to fend off an unexpected challenge in the next states to vote.

Santorum countered that Romney, the front-runner in the GOP presidential race, "should not be our nominee" because he was "dead wrong on the most important issue of the day" when, as governor, he signed a health care overhaul into law in Massachusetts.

The two sparred from afar one day before Republicans in Colorado and Minnesota hold nominating caucuses, the latest contests in what's become almost a plodding race for the GOP nomination compared to the rapid-fire campaign of last month. Newt Gingrich and Ron Paul also are competing but neither was expected to have a breakout performance in either state.