Pretty clear signals here that the US will support Taiwan under Biden.
On the other hand, Trump abandons allies like the Kurds whenever Uncle Putin asks him to.
I once saw a former White House Security advisor interviewed on the topic. He was retired Military brass who had worked for the Obama administration. The interview was early on during the Trump Presidency.
They posed the question to him, what would the US do if push came to shove over Taiwan. His response was that it was useful for China to think that the US would intervene militarily in a physical sense. But reading between the lines he seemed to be suggesting it was bluff.
This he noted was essentially a bipartisan policy of what he referred to as more conventional Presidencies (as in, Obama, Bush, Clinton all held very similar positions). So what you see in Biden’s messaging isn’t so much a definite “we are backing Taiwan if it came to the absolute worst.” But it’s a return to the messaging of previous Presidencies, just trying to sow seeds of doubt in China’s mind.
In the interview he was deciphering between what he called “conventional” Presidencies and a Trump Presidency. He commented that the same assumptions are all thrown out the window under a Trump Presidency. On national security Trump was so inconsistent, chaotic and incoherent there was no way to possibly predict what his policy was towards Taiwan. It would probably depend on which way the wind was blowing on the day.
And that is the consistent account of Trump on security policy from a range of military brass who have worked closely to, or in the White House with him. Even those of the more hawkish-right wing mould were very alarmed by how superficial his understanding was on issues to do with security. And how he appeared to have little interest, desire or attention span to delve into and actually understand in any depth, the ins and outs of foreign and security policy he was being advised on.