Putin isn't going to invade Ukraine, stop wringing your hands. This is just typical probing of a new administration to gauge our response and appetite for a fight. You guys give Putin and Xi way too much credit - Putin does not want a war with Ukraine, he is playing from the back foot here because his 2014 invasion obviously pissed off Ukraine who now actually want to join NATO, a disaster and embarrassment for Russia. Putin is just throwing his tanks around to try to get some commitment from Biden re Ukraine never joining NATO or giving away some territory in the east. This is the same reason Russian separatists continue to occupy a corner of Ukraine - Ukraine can never be admitted to NATO while some of its territory is occupied by Russia, and Putin know this. But a full invasion of Ukraine would be a disaster for Russia - not that they would lose, but its a massive country with a serious military and obviously a good portion of the country would fight bitterly. This is without any US involvement. Putin just wants his near term guarantee on no NATO and no western forces in Ukraine, and in the process to gauge our appetite to fight for Ukraine (it's zero). He will no doubt invade when the China do something to merit our full attention, but he isn't going to start shit now - the guy isn't a risk taking clown like Bush.
China is the much bigger worry. The economy seems to be decelerating and unlike in Russia, this is not the standard state of affairs the Chinese people or party appatichiks are accustomed to. Xi is not in anywhere near as strong a position as many people assume and this is very dangerous because there are no doubt members of the party who want his scalp a and a slowing economy only gives them ammunition, so Xi may need a win on his CV in the next few years. That said, there is no clearer or more obvious path to Xi's own downfall than a botched invasion of Taiwan, so he obvious needs to be quite careful as well. I do not think he moved in the near term because its obvious Xi and the party at large believe their own propaganda regarding american decline and expect to have a stronger hand in the near future. Give it 5 years and that's when things will get really dicy - Xi will still be in the chair but the economy will be half a decade into the new, slower growth, reality. It's military will be significantly more capable and god knows where the US will be at that point. Trump could very well be in office 2024-2028 and USA hosts World Cup in 2026 and Olympics in 2028, the timing for a Chinese stunt just seems to appropriate. China will not invade outright, they will probe and probe until its clear we do nothing. I could easily see them sailing a massive fleet within 30 miles of taiwan during WC or Olympics, and then just parking it there and saying good luck forcing us out. They won't shoot and we won't shoot, and we will get used to a huge armada siting off taiwan.
Rememberer the USA is buck wild and we have redlines as well and frankly no one has a clue where they are. If you think we are scared of the Russian or Chinese nuclear arsenals - well lets just say we are the only country to have used nukes in war to date and are almost certainly the most likely country to use them again. Foreigners have rightful reason to be concerned americans have an itchy trigger finger and this is why the tactics employed by Russia and China are always sub scale shit like cyberattacks - they know the US has an extreme capacity for war if the populace is given a political reason to wage one. Russia and China do not want to create that reason, and they will continue to probe us until they have some assurance that invading Ukraine or blockading Taiwan will not result in a political consensus for war. Both of these nations probably rightfully think the US is best left fighting itself, which we are proceeding with quite well at the moment, and that uniting the country in a war against a common enemy would be a huge strategic blunder. It's interesting because if you read the academic commentary the appropriate US response is quite clear - containment, cold war style. Like the soviet union, both Russia and China feel they can prevail by simply biding their time, eventually the US will collapse upon itself and then they will have a free hand. We would take the opposite approach - overtime the authoritarian regimes in russia and china will collapse as they fail to deliver economically and innovate. I'm not sure the US would have made this same calculate re China 5 years ago - but with Xi up to his Maoist nonsense, I think the US is much more confident we can prevail long term. But Chinese and Russian machinations must be met with force. Putin must realise the only consequence of Russian troops in Ukraine will be US troops in Ukraine. China must realise we can and will drive up the cost of any Taiwanese invasion to extreme levels.