The hardest part of building nukes is acquiring weapon-grade enriched uranium, because it's controlled as hell and you will get bombed if you try to make your own.
If you spend hundreds of millions of dollars on enriched uranium, paying salaries for team of engineers is the easy part.
There is a rumor that the USSR flirted with the idea of a pre-emptive strike on Mainland China to decapitate their nuclear program after the Sino-Soviet split. This did not happen obviously.
Iran didn't get bombed, although that may just be because other forms of sabotage were available.
Syria & Iraq on the other hand, yeah those got bombed. But it's not 100% a guarantee.