Rebuke came as former reality TV host closes in on clinching the Republican nomination

US President Barack Obama cast Donald Trump's positions on immigration, trade and Muslims as part of an ignorance-and-isolation philosophy that the president said will lead the United States down the path of decline.

Obama used his commencement speech on Sunday at Rutgers University to tear into the presumptive Republican nominee, without ever mentioning his name. Time and again the president invoked specific Trump policies to denounce a rejection of facts, science and intellectualism that he said was pervading politics.