Invasion of South Korea by the North ?

The Times: Reports on the prospects of a North Korean invasion of the South. A quick invasion and the taking of Seoul might not be that mad, North Korea has a million man army, South Korea has the better trained US Armed Forces and equipment, but a million man army could just be to much for South Korea. What if the North can take control of the South, what would the Obama Administration do, could they repel the North with conventional forces, problem they are stuck in Iraq and Afghanistan, would Obama go nuclear, have my doubts, so you see not that mad. This is why Obama has to get tough with North Korea, he might look weak and the North could just march in to the South, the Obama Presidency would be over before it started, he would be the President that lost South Korea to a Stalinist North Korea.