No, you cannot reenter the US without a passport.
Yes, but you will not be able to reenter the US without a valid passport. (source below)
The US now requires a passport, passport card, or enhanced drivers' license to reenter the US from Mexico or Canada. Persons crossing into those countries will be checked for those documents to ensure they have the necessary documentation for return.
Yes, Haiti is an independent country.
The US passport is what you need to get back in. Unless you're already outside the US, I wouldn't leave until you have this important document. Technically, you could just reenter the US as a Canadian tourist with a Canadian passport under the VISA Waiver programm but why chance it?
If you are coming from abroad then yes, you still need your passport. The passport is a very important travel document which you should always carry when you travel in and out of the US.
No, you cannot enter the US without a passport.
No, you cannot leave the US without a passport.
No, you cannot re-enter the US without a passport.
No, you cannot come back to the US without a passport.
No, you cannot travel outside of the US without a passport.
No, you cannot travel outside the US without a passport.
No, US citizens cannot travel internationally without a passport.