Yes, it does become invalid. Ask the passport office to see if it makes the passport valid if you sign it again. Otherwise you may need to apply for a new one.
Yes, they definitely need a passport to legally enter the United States.
Answer you need to get a passport
No ANSWER: Because both locations are in the United States, you will not be required to have a passport. Travel within the continental United States does not require passport.
If you are flying within the United States, you do not need a passport. If you are flying into the United States from another country, or out of the United States into another country, you need to present a passport at customs.
yes u have to have a passport to travel anywhere out of the united states
Not from United States.
If you live in the United States, no.
United States Department of State
You don't need a passport to travel within the continental United States, even if you are not a citizen.
If where you want to go is out of the United States you do need a passport, but if it is within the 50 states no. We are not little countries with borders, but the "united " states. That means we are one country.
No, if you are in the United States, you will need to obtain a USA passport to go to another country or to return. Within the 50 states, you will not need a passport.
Yes, but only in Mexico, not in the United States. You will need either a US passport or a green card/work permit to work in the United States.