George W Bush invaded Iraq to remove its - ultimately nonexistent - weapons of mass destruction. Barack Obama used cyber weaponry and sanctions to deter Iran from building its own atomic bomb. Now Donald Trump faces North Korea, but stopping its nuclear and missile program may prove impossible, creating what may be his first and perhaps defining international crisis.
Trump has been left to confront North Korea's nuclear activities because his predecessors failed to manage them. The regime in Pyongyang, meanwhile, continues to build ever more dangerous - and hard-to-destroy or intercept - weapons systems.
North Korea has been a thorn in the side of the United States since the days of Harry S. Truman. The Korean War came dangerously close to sparking a nuclear confrontation, with the White House preventing U.S. commander Douglas MacArthur from using atomic weapons to stop the Chinese and North Korean armies. Under Pyongyang's current leader Kim Jong-un, it is reaching what may be its most dangerous point since then.
Washington's foreign policy establishment has a host of disagreements with Trump. They think he is wrong on immigration, too soft on Russia, too dangerously hawkish on China. On North Korea they are in the same hole as he is with no real ideas about how to get out.
This is a crisis everyone has seen coming. That's why Japanese Prime Minister Shinzo Abe has been so desperate to court Trump, visiting him even before the inauguration. As North Korea launched an intermediate medium-range ballistic missile on Sunday, Abe was once again with the president - this time on a golf and bonding trip to Mar-a-Lago, Trump's Florida retreat.
It's also why U.S. Defense Secretary James Mattis made his first official trip to the region. His priority was to reassure Japan and South Korea in particular that the United States would stand with them - whatever noises Trump made during his election campaign.
Pyongyang first demonstrated its ability to detonate a crude nuclear device in 2006 - becoming the only Iraq- or Iran-style "rogue state" to ever get that far. Since then, it has continued to develop not just the bombs but also the missiles to deliver them.
Ultimately, the regime would love to have the ability to strike the continental United States - a prospect Trump has tweeted to say "won't happen". For now, however, there are few signs anyone has a plan to stop it.
It's not that Pyongyang has ambitions to launch some kind of unilateral strike - that would be suicidal. What it wants is a deterrent to protect it from any kind of Iraq- or Libya-style "regime change".
To achieve that, it first needs a limited number of land-based nuclear-tipped rockets with the ability to strike at least as far as Japan. Each test brings that goal closer.
In the slightly longer term, it wants to be able to mount rockets and warheads on a small fleet of diesel electric submarines. These could be positioned offshore or along its mountainous coastline, hard to track and destroy and - because of the unpredictability of their locations - harder to intercept should the rockets one day be launched.
Nothing the United States has done has seriously frustrated that ambition. In the aftermath of the Iraq invasion, Bush had limited success in using financial aid - and the threat of greater sanctions - to persuade Pyongyang to slow its program, even demolishing a cooling tower at the nuclear facility in Yongbyon.
That still wasn't enough to stop the 2006 nuclear test. And with the accession of Kim Jong-un after the death of his father in 2011, North Korea has been much more single-minded in its atomic ambitions.
Following the apparent success of the Stuxnet computer worm against the Iranian nuclear program, there are suggestions the Obama administration tried something similar against North Korea, but the attempt was much less successful. Such covert activities have likely continued, but they may not be enough.
Since Bill Clinton in the nineties, successive U.S. presidents have been presented with options for more direct action such as air and missile strikes. How successful they would be, however, has never been clear. Pyongyang has no shortage of ways in which it could respond, not least through using conventional artillery to strike U.S. and South Korean targets. The South Korean capital, with its population of more than 10 million, is firmly in range of North Korean guns which, like its nuclear program, are believed to be stored in deep, hard-to-destroy bunkers.
One option now on the table would be for the United States to attempt to intercept a future North Korean missile test with some of its anti-ballistic missiles in the region. That didn't happen on Sunday, perhaps in part because that test occurred over a relatively short distance, mostly over or near North Korean territory.
Attempting to shoot down a longer-range missile test would be easier - but the success of such an action could never be guaranteed. If it failed, the United States would essentially have advertised its inability to intercept a North Korean missile, sparking even greater concern in the region.
The political fallout of a botched intercept would also be significant for any U.S. president.
That leaves diplomatic options, such as applying pressure through China. Beijing's economic support for North Korea is vital to its survival, and the topic was likely high on the agenda during Trump's first call with the Chinese premier. But China is reluctant to do anything that might bring about the collapse of the regime and potentially put South Korean or U.S. troops on its border.
Beijing has also long argued that anything it did to undermine North Korea might hasten the unraveling of the regime, bringing with it the danger that Pyongyang might lash out, perhaps with nuclear force.
There are a variety of potential targets for North Korea even if it cannot reach the United States. They include regional U.S. bases such as Guam as well as South Korea. Many experts believe a Japanese target might be the most likely, not least because of lingering resentment over atrocities in World War Two.
In time, that threat might be enough to prompt Tokyo to acquire its own nuclear arsenal - something that would antagonize Beijing, and arguably make the region even more volatile.
Trump may see himself as a master of the "art of the deal", and has raised the prospect he might meet North Korean leaders. His problem is that there may be no deal to be done. This situation may become more dangerous - perhaps until something truly cataclysmic happens.© (c) Copyright Thomson Reuters 2017.