51% of respondents say North Korea is a "direct threat" to the United States. 46% say the same thing about Iran.
The poll was conducted on Monday and Tuesday, just as the protests in Iran were building. I'd be curious to see how the growing unrest in that country affects Americans' perception of the Iranian threat.
Gallup helpfully breaks down responses by party ID. Republicans are much more likely to see global threats than Democrats are, with independents somewhere in the middle.