SINGAPORE — President Donald Trump and North Korean leader Kim Jong Un shook hands at a summit in this city state, a landmark moment in an ambitious and uncertain bid to bring about nuclear disarmament.

The two men, who spent months trading insults, settled in for what was expected to be hours of meetings — aides said no time limits had been set — at about 9 a.m. in Singapore on Tuesday, or 9 p.m. Eastern time Monday.