With a characteristic sense of timing, Pyongyang set off its underground nuclear test as Obama polished a new call for action at home to tackle high unemployment and economic headwinds threatening the fragile recovery.[break]
Less than a month into his second term, the president will step up to deliver the annual showpiece speech in the House of Representatives, and before a huge national television audience at 9:00 pm (0200 GMT).
Obama will strike the populist message that helped him defy tough times to win re-election in an address largely aimed at a domestic audience -- a down payment from the stock of political capital he piled up in November.
But North Korea´s test also presents Obama with a foreign policy headache in Asia, as Pyongyang shrugs off sanctions which have kept it in deep isolation to stride closer to full membership of the nuclear club.
Obama had already been under fire from political opponents over another nuclear imbroglio, with Iran, as he argued for more time for punishing sanctions to convince the Islamic Republic to halt its atomic development.
Ironically, Obama had been expected to renew his core commitment to seek cuts in global nuclear weapons stocks, which has been at the core of his foreign policy, during his speech on Tuesday.
North Korea´s action once again revealed Pyongyang´s penchant for using big events, like major Obama speeches or a current transfer of political power in South Korea, to issue a flamboyant demand for attention.
It also came as Obama nominees Chuck Hagel and John Brennan await confirmation votes to be the next chiefs of the Pentagon and CIA, after encountering opposition from Republicans.
The president will still likely use the bulk of the State of the Union speech to lay out a governing program to match the soaring progressive vision of his inaugural address last month, drilling down on the haunting jobs crisis.
"The President has always viewed the two speeches, the inaugural address and the State of the Union, as two acts in the same play," White House spokesman Jay Carney said, before word came of the North Korean nuclear test.
"The core emphasis that he has always placed in these big speeches remains the same and will remain the same, which is the need to make the economy work for the middle class."
Obama will refresh some plans he has already framed for creating jobs, including investment in America´s ageing infrastructure -- which never made it past Congress -- and offer some new ideas.
But the speech will take place in the shadow of Obama´s row with Republicans over huge budget cuts due to hit in March 1, which could hammer the fragile economy.
There are new reasons for alarm over the flat economy, after GDP contracted at an annual rate of 0.1 percent in the last quarter of 2012 and the unemployment rate ticked up to 7.9 percent.
The White House argues, however, that there is no comparison between the howling crisis that Obama inherited four years ago and the economy of today, although it does not dispute that many Americans are still hurting.
In a new Quinnipiac University poll released Monday, 53 percent of voters said they believed the economy was in recession, and 79 percent described it as "not so good" or "poor."
But Obama was still trusted, by 47 percent to 41 percent, to handle the economy better than Republicans.
While jobs will be his prime focus, Obama is also likely to highlight other domestic issues, though he knows Washington´s bitterly partisan climate could render many big plans dead on arrival on Capitol Hill.
One priority will be building support for new laws to curb gun violence, after the horror of December´s massacre of 20 small kids at a school in Newtown, Connecticut.
First Lady Michelle Obama will host in her box in the House the parents of Hadiya Pendleton, a teenager gunned down in a random shooting not far from the president´s Chicago home days after she took part in his inaugural parade.
At least 23 members of the House will also host gun violence victims. Among them will be US lawmaker Gabrielle Giffords, who suffered brain damage after a gunman opened fire at one of her political events in 2011.
Natalie Hammond, a teacher who was shot three times by the Newtown gunman, will also be there.
Aides said Obama will also make a pitch for immigration reform, the centerpiece of his second-term agenda, amid signs that Republicans keen to mend fences with Hispanic voters may be ready for some rare cross-party compromise.
He may also note the impending return of the remaining 60,000 US troops in Afghanistan in 2014, but it is unclear whether he will offer more details on the pace of their withdrawal.
International sanctions on North Korea
North Korea´s nuclear test is likely to result in the imposition of new or tightened sanctions by the UN Security Council, which had warned of "significant action" if Pyongyang went ahead.
The North´s missile and nuclear programmes have attracted waves of sanctions over the years, including multilateral measures announced by the UN and penalties by individual countries.
Here is a roundup of measures currently in force:
UN SANCTIONS
The UN Security Council sanctions have been imposed and expanded over a series of four resolutions dating from a missile test in 2006. They cover the North´s two previous nuclear tests in 2006 and 2009 and long-range rocket launches in 2009 and last year.
The sanctions currently commit all UN member nations to:
-- A total embargo on the supply, sale or transfer of arms and arms-related material to North Korea and the procurement from North Korea of the same.
-- A ban on imports and exports from and to North Korea of certain goods and technology listed by the UN.
-- A ban on exports of luxury goods.
-- Freezing the funds and economic resources of North Korean entities listed by the UN.
-- A travel ban preventing any access to individuals listed by the UN.
-- Cooperative action to prevent illicit trafficking in nuclear, chemical or biological weapons, ballistic missiles and their means of delivery, related materials and technology.
UNITED STATES
The United States has its own sanctions that involve seizing the assets of any individual or entity deemed to be assisting North Korean arms trafficking, money-laundering, counterfeiting, bulk cash smuggling and narcotics trafficking.
US citizens are banned from registering vessels in North Korea.
Imports of any goods, services, and technology from North Korea require a government licence.
EUROPEAN UNION
On top of the UN sanctions, the EU has its own list of items subject to an export ban, and of people and entities subject to a travel ban and asset freeze.
It also operates enhanced vigilance of the activities of EU financial institutions with banks domiciled in North Korea and reinforced cargo inspections.
SOUTH KOREA
Following what it said was the sinking of a South Korean warship by the North in March 2010, Seoul unilaterally banned all inter-Korean trade and South Korean investment in the North.
The only exception was a joint-venture industrial zone set up on the North Korean side of the border in 2004.
AUSTRALIA
Australia has targeted financial sanctions implemented by its central bank. They include restrictions on financial transactions involving entities or individuals associated with North Korea´s nuclear and missile programmes.
It also operates a general ban on visas for North Korean nationals and bans port access to North Korea-flagged vessels.
JAPAN
Japan Tuesday began strengthening its unilateral sanctions. Prime Minister Shinzo Abe said Tokyo would tighten immigration controls on the staff of a major pro-Pyongyang organisation in his country.
Sanctions imposed after nuclear tests in 2006 and 2009 include banning all exports to and imports from the North and barring its ships from Japanese ports.
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