The continuing fragility of the Romney candidacy was emphasised by reports in Washington political circles that senior Republicans are still drawing up emergency plans to introduce an eleventh-hour alternative candidate if Mr Romney loses in Michigan.
One "senior Republican senator" quoted anonymously by ABC News said the party would have no alternative but to seek another candidate, dismissing Mr Santorum, who is an evangelical Roman Catholic as a man who would "lose 35 states".
"If Romney cannot win Michigan, we need a new candidate," the unnamed Senator was quoted as saying, adding he would call publicly for a 'saviour' figure to step forward in the form of Jeb Bush, the younger brother of George W Bush and two-term former governor of Florida.
However other senior Republicans cooled such speculation yesterday observing that time was running out for any new candidate, as filing deadlines approached for the nine primaries and four caucuses that begin in Michigan on Feb 28 and end with 'Super Tuesday' on March 6.
Mr Santorum, meanwhile, continued his appeal to blue-collar, religiously conservative voters while campaigning in the critical Rust Belt state of Ohio over the weekend, attacking Mr Obama for an agenda based on a "phony theology" and "not a theology based on the Bible".
The former Pennsylvania senator later clarified his statement, telling CBS's Face the Nation that he was not attacking Mr Obama's religious faith, but his environmental beliefs that put the needs of the earth before people.
The White House said the remarks were 'a new low'.