Even if it's only pre election gibberish some hardliner in China, Russia, Iran or North Korea might be inclined to put his words to a test.
It's absolutely reckless to even play with such threats in the election campaign.
It's his way to tell the European countries to step up to the plate when it comes to NATO.
Take a closer look at the West lead by the US behaved across the world in the past 75 years and I'm sure you'll understand what I'm getting at.
Taiwan isn't a NATO member as well. If Trump abandons the Ukraine and leaves Europe alone, do you think European countries will come up to support the US on Taiwan, if China dares to escalate?
Again Trump is playing with fire here.
India, Japan, Australia and South Korea could fill in the gaps. But Europe would better fall in line and will do it, for their own sake.
Taiwan's economy is four time Ukraine's, a major thoroughfare for worldwide shipping and more importantly the main supplier of semi-conductors (about 70%) and advanced microchips (around 90%) in the world. Furthermore, you have the strategic position Taiwan occupies in the "First Island Chain", a vital cog in the defense system of the Philippines, Japan, and South Korea. China taking over Taiwan and controlling the Taiwan strait would give it the capacity to project its evergrowing Navy deep into the Pacific ocean, and directly threaten all the US allies in the region, something they aren't able to do right now.
Long story short, from a US point of view, Ukraine is expendable (kinda), Taiwan is not. Unless the West, particularly the US, wants to give China, which is the real competitor, the keys to the Indo-Pacific, an even greater part of the world economy's pie and look like real clowns. That's something even Trump understands.
Frankly, I was also in the camp thinking Putin was only bluffing and would never ever attack the Ukraine. Februar 24th proved me and many Germans to be totally wrong. Since then I wouldn't exclude anything when it comes to Putin. He left the rational path a long time ago.
Putin is a thug but a very rational one.
He's always been particularly fixated about Ukraine's place on the European chessboard, which was an open question since 1991. He considers it as part of Russia's backyard, a bit like Mexico for the US, for historic, economic and strategic reasons. Don't forget that all major invasions of Russia from the West went through Ukraine. He's determined to bring back Russia into the major league with a (big) say in world matters and never forgot the humiliation of the fall of the Soviet Union and its disastrous consequences. He repeatedly made it clear that any further attempts from Ukraine to get into NATO or encouragement from the West would trigger a Russian response. That Russia wouldn't bow down, to use your own expression. The West thought that he wouldn't do it. Until he did.
I'm not justifying what he did, it's wrong on every level, every country has the right to self-determination and choose its own path. But a demented idiot, Putin is not. People should be wise to that.