If you want countries to stop become Nuclear enabled, then you have to increase the costs, and decrease the rewards for doing so. No President did more harm to that cause than Barack Obama: Libya, Ukraine, Iran, North Korea, it was a shit-show of incompetence.
Remember the goal, increase the costs, decrease the rewards, not hard.
- Ukraine had made a global treaty with the UK, Russia and the U.S. that they would give up their Nuclear arms as long as the others agreed to defend them if they were attacked or invaded by Russia. Everyone said, "we'll be there". So Russia invaded Ukraine (first Crimea, then in a sponsoring at aiding rebels in east Ukraine). Even shooting down civilian aircraft. The Obama Administration's response to this bad behavior? He refused to support Ukraine, or even send them weapons. Trump immediately started extending military supplies to the opponents of Russia, which is why the left claims that Trump is a puppet of Putin (because like that, Syria and other things, he did everything he could to weaken them and strengthen our position).
- In Libya, we promised Gaddafi that if he stopped sponsoring terrorists, helped us find them, and stopped his Nuclear weapons program, then we wouldn't bomb him. He did all of that and he went from one of the biggest terrorist sponsors, to one of our most important allies. So the Obama administration aided in his overthrow and murder, which taught the world that giving up your Nuclear ambitions will not only weaken your military power in the region, but will be an invite for the U.S. to break it's promises and have you murdered.
- In North Korea, the Clinton administration especially (but the Obama administrations as well, and the Bush administration to a lesser extent), believed that the solution to North Korea getting Nukes and threatening to expand their program, was to reward them: pay them to slow down development. Then the North Koreans would speed up development and do more displays, and Obama/Clinton agreed to pay them more to slow down (aka, keep doing it).
- In Iran, Obama flew over plane-loads of money, for them to spend on their Nuclear program, as long as they agreed to shut down a few public efforts -- but they could continue secret efforts on bases we agreed not to go into, and even the public ones we could only visit after giving them weeks of notice, and if they felt like saying "yes" to. This was a way of telling despotic regimes that they extort billions on a reoccuring basis, if they stoke their Nuclear ambitions. (Increasing the reward is encouragement, no matter the intent).
- Iran going Nuclear and the weakness of our efforts to stop them, told others in the region that they too needed to be Nuclear powers, or they'd be the victims of an aggressive Iran and a feckless U.S. -- and Saudi Arabia and others said as much, and re-started their efforts. They would have been stupid not too.
No matter the intent, the Obama administration did more to undermine nuclear de-proliferation than anyone since Kruschev. Even if the Obamabots cant do 1+1.