Can you re-enter the US under the visa wavier program a few days before the 90 days VWP limit expires? I traveled to the US for one week back in May and was wondering if I can now return to the US for 3 weeks a few days before the previous entry stamp expires. Is a new stamp issued on the passport or do I have to wait until the old one expires before trying to return?
The US 90-day clock works differently than in the EU. It resets as soon as you leave North America. So you should be fine to come back for up to another 90 days, provided the CBP officers don't have reason to think you are trying to immigrate illegally...