The fierce in-fighting among Republican presidential challengers intensified ahead of Tuesday’s Illinois primary with Rick Santorum unleashing one of his most personal attacks yet on frontrunner Mitt Romney.

Santorum, scrambling for votes as the latest poll showed Romney with an overwhelming lead, claimed Romney had “no core”, was being bankrolled by Wall Street and would be unelectable against Barack Obama.

Such outbursts play into the hands of the Democrats, providing material they can use during the White House race between Obama and the eventual Republican contender, almost certainly Romney. Polls also show that the in-fighting is turning off independent voters, the key to the general election.