Influential Iowa conservative activist Bob Vander Plaats called this evening for Michele BachmannMichele Marie BachmannBoehner says he voted for Trump, didn't push back on election claims because he's retired Boehner: Trump 'stepped all over their loyalty' by lying to followers Boehner finally calls it as he sees it MORE and Rick Perry to drop their bids for the Republican presidential nomination in order to maximize Rick Santorum's chances of defeating Mitt Romney in a one-on-one matchup.

"The last thing Mitt Romney wants is to go one-on-one with Rick Santorum," said Vander Plaats, who endorsed Santorum in December. "He wants to have a multiple-candidate field. So I think some of these candidates need to reassess where they're at tonight."

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When The Hill asked "Like who?" Vander Plaats, president of group The Family Leader said it should be "painfully clear."

"I think Michele Bachmann has to, definitely. We love Michele Bachmann, we love all the issues she stands for. I just think the message is going to be loud and clear tonight," he said. "We did this drill four years ago. Had Fred Thompson not stayed in the race in South Carolina and taken 9 percentage points, Huckabee wins South Carolina."

This scenario, he suggested, could have resulted in Huckabee becoming the nominee.

Vander Plaats added that Perry had to undertake a similar "reassessment".

Saying that it looked like Perry would take about 10 percent of the vote, he suggested that might be the Texas governor's ceiling.

"I think it's a reassessment for him as well," he said. "Even if he has a lot of resources to go on, he pumped a lot of resources into the state of Iowa and he went from 10 to 10. What that tells you is that people are making up their mind already on Rick Perry."