I’m an Italian citizen visiting the US with an ESTA. I want to go to Mexico for a day trip with some friends and then go back to the US.
We’ll cross into Mexico from San Diego by land and go back the same way.
I have a plane from San Diego to Italy a few days later and my 90-days stamp will still be valid for more than 2 months.
Will I have any problem?
There is no issue with your Visa Waiver when you enter by land. According to CBP you don’t even need ESTA. So as long as your Waiver clock still has some time on it see here or here you should not have an issue.