All along he's been trying to trade bomb capability for nuclear power.
And as long as Clinton lived up to the agreements, so did he. Shut down his research, allowed inspections.
Bush came along, told him to give everything up for nothing, dishonored the agreements (why should this have been any different) and Kim started up again.
Simple.
However, that's not the Conservative spin. You'll hear differently from the same people who brought you Iraqi nukes, Iraqi WMDs and are bringing democracy to Iraq and Afghanistan. THOSE people have their own version of screwing up the North Korea nuke deal.
Arf