"Your [Republican] party's nominee for president was kissing up to [Russian President Vladimir] Putin, the former KGB officer," Obama said while campaigning for Clinton at Miami Gardens in Florida on Thursday.
Obama ridiculed Republicans for supporting a presidential candidate who had repeatedly advocated having good relations with Russia and its leader.
"You [Republicans] are OK with your nominee having a bromance with Putin," he added to cheers from his audience.
In his debate with Clinton on Wednesday night, Trump said he had never met Putin and repeated his previously expressed opinion that good relations between the United States and Russia were desirable. Trump has also called for cooperation with Russia in fighting the Islamic State terror group.