It could happen in Russia, and somebody like a major general or a one-star general or colonel will come to power without any international experience. If such a person would come to power, pushing the nuclear button would be no problem. A few months. You have to remember that the Russians have the same number of submarines, nuclear missile submarines, ships, bombers, fighters, tanks and the like as they did at the height of Soviet military power. I know that Russian military downswing was connected with Army divisions only, and these divisions could be rebuilt in weeks or months.
China has the largest conventional army in the world.
If China and Russia would ally in a war against the United States, with Russia providing the strategic weapons and China the troops, they could begin the war tomorrow. Recent press reports state that the Russians have been helping the Chinese develop ballistic missile technology. So the Soviet Union, let's say, played the major role in the establishment of the Chinese missile industry. But this was in the '50s before the Sino-Russia split. This split was healed in the late 1980s and any ideological obstacle for helping China was removed.