Santorum: If you like Romney, vote for Obama

(CBS News) Republican presidential candidate Mitt Romney's top strategist estimated Thursday that rival Rick Santorum would have to win over two-thirds of the remaining delegates in upcoming primaries to secure the minimum needed for the nomination, and he suggested that Santorum's continued presence in the race makes him President Obama's "most valuable player."

As the campaign rhetoric grew increasingly testy between the two camps, Santorum said that Romney is so much like Obama, voters in the fall might as well stick with the incumbent. At a campaign event in San Antonio, Santorum reprised his ridicule of the front-runner as the Etch A Sketch candidate, who will change his positions after the primary.

"You win by giving people a choice," he said. "You win by giving people the opportunity to see a different vision for our country, not someone who's just going to be a little different than the person in there. If you're going to be a little different, we might as well stay with what we have instead of taking a risk with what may be the Etch A Sketch candidate of the future."

The Romney campaign fired back, "I was disappointed to hear that Rick Santorum would rather have Barack Obama as president than a Republican. This election is more important than any one person. It is about the future of America. Any of the Republicans running would be better than President Obama and his record of failure."

In a campaign memo circulated to reporters, Romney Political Director Rich Beeson wrote that Romney won all but 13 of the delegates at stake in Puerto Rico's primary on Sunday and in Illinois' primary on Tuesday. That gives him a total of 563 delegates to Santorum's 263, putting him ahead by 300 delegates, according to the Associated Press delegate count - a lead touted by Beeson in his memo.

"In order for Senator Santorum to secure the 1,144 delegates needed to win the nomination, he must win 70% of all remaining delegates," Beeson said, noting that Romney is more than half way to the magic number.

"The remaining contests offer no path to 1,144 for Senator Santorum, a fact which even he has acknowledged," he writes. "Each day Senator Santorum continues to march up this steep hill of improbability is a day we lose to unite in our effort as Republicans to defeat President Obama. So as Senator Santorum continues to drag out this already expensive, negative campaign it is clear that he is becoming the most valuable player on President Obama's team."