The United States. Okay, we don't threaten ourselves. But sky-high budget deficits and an unwillingness to raise taxes an iota will inevitably lead to cuts in spending on defense and intelligence (the only question is whether we'll use the sequestration axe or a more sensible scalpel). Perhaps even more important, the American people may be reluctant to make sacrifices to ensure we have a robust foreign policy. Support for foreign aid gets lower and lower, and grinding wars in Iraq and Afghanistan have made Americans wary (often appropriately) about the risks of intervention. We will still have a massive military and international presence, but we will have fewer resources than before and may be less willing to use them. We cannot think about threats abroad without recognizing how our problems at home will shape our response.
Where Iran ranks on this list is an open question. The clerical regime in Tehran is openly hostile to the United States and its regional allies. Yet its leadership seems more rational than what we've seen in North Korea, the country is less chaotic than Pakistan (to say nothing of Syria), and of course its military and economic power are a pale shadow of China's. None of this means Iran can be ignored, but it also means that as we evaluate candidates we need to think beyond the crisis of the moment. We also need to recognize the limits on our power, and any president will have to decide how much to push the American people in pursuit of his foreign policy objectives. Some, perhaps all, of the challenges above have no good solutions (and often we'll only know what was a foolish idea in hindsight), but all of them deserve scrutiny as candidates present their case to the American people that they can best keep our country safe and ensure that the United States remains a world leader.
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