A speech by Barack Obama adopting the mantle of working-class champion and branding the Republicans as the party of the rich has been welcomed by the left and denounced by conservatives.

On Tuesday night, the president set out what is likely to be one of the major themes of the 2012 campaign: growing inequality in the US. He was speaking in Osawatomie, Kansas, the same town from which Theodore Roosevelt called for a square deal for the American people a century ago.

“This is the defining issue of our time,” said Obama. “This is a make-or-break moment.