President Obama went to Hiroshima, did not apologize, did not state the facts of the matter (that there was no justification for the bombings there and in Nagasaki), and did not announce any steps to reverse his pro-nuke policies (building more nukes, putting more nukes in Europe, defying the nonproliferation treaty, opposing a ban treaty, upholding a first-strike policy, spreading nuclear energy far and wide, demonizing Iran and North Korea, antagonizing Russia, etc.).
Where Obama is usually credited -- and the reason he's usually given a pass on his actual actions -- is in the area of rhetoric. But in Hiroshima, as in Prague, his rhetoric did more harm than good. He claimed to want to eliminate nukes, but he declared that such a thing could not happen for decades (probably not in his lifetime) and he announced that humanity has always waged war (before later quietly claiming that this need not continue).