Barack Obama said on Thursday he had raised a record-breaking $32m in January, a powerful demonstration of his ability to stay in the race beyond next week’s Super Tuesday vote and all the way to the Democratic convention in August if ­necessary.

The race looks set for a war of attrition after February 5, with Mr Obama and Hillary Clinton battling it out state-by-state through the remaining 23 primaries and caucuses that fall between next week and early June.