Of course each of these countries are ignoring international law in various respects and doing things in their self interest.
Anything as brazen as capturing a president? Not yet. But I can absolutely see them doing this if they deem the cost/benefit great enough.
I wouldn't be surprised if China goes further and launches a full-scale invasion of Taiwan in the next decade, they've certainly been preparing for it according to our intel.
Why wouldn't China do the same in another country whose president is not acting in China's national interest? If you were Iran[1], would abandoning your nuclear weapons program for sanctions relief still be an option?
1. Or Saudi Arabia