US President Barack Obama on Thursday said that global leaders are "rattled" by some of presumptive Republican presidential nominee Donald Trump's policies, blasting the ideas as demonstrating "ignorance" of how the world works. Trump, the billionaire US real-estate mogul and reality TV star, has dominated headlines since launching his presidential campaign last year with a mix of incendiary comments and policy stances seen as insulting Mexicans, Muslims and women, among others.