Mitt Romney: 'Beginning of the end of the Obama years'
Republican presidential hopeful Mitt Romney has called for a focus on President Barack Obama and vowed to build "a better America".
Mr Romney spoke as he racked up a series of primary wins on a night with most electoral delegates at stake since Super Tuesday.
In a speech seen as opening his general election campaign, the former Massachusetts governor said Barack Obama had done his best, but America could do better.