^ I must agree with OP if Biden will be the president and be able to create a higher demand on dollars then definitely it will make their currency stronger however it might slow down the recovery of their economy for citizens will need to consider the usage of their dollars and if so, it will create slow to moderate movement in the market which may weaken the economy. Nevertheless, this can still be speculative since we have not seen the real platforms of Biden and how he can put it into actions but once he became the president he will then know what are the things he needs to put into considerations before implementing his platforms
No one can print dollars indefinitely
Neither Trump nor Biden. It works pretty much like the law of diminishing returns. In fact, this is the law itself. In more concrete terms, sooner or later new money will make inflation unbearable, and that will mean the turning point (you can also think of it as a point of no return, in a sense) after which more easing will only do harm to the economy. If it weren't so, every country could easily print their way out of any economic predicament they get into. It doesn't work like that, see the Zimbabwean dollar and its dark fate as an illustrative example