Airlines will not let you board without the proper documentation, ie: passport, period, end of story. The reason being is that public carriers can get fined if you are not eligible to enter the USA and they transport you there.

Trains and buses are also public carriers and are supposed to document that you have permission to cross the border before boarding you.

The "I am a US citizen and you can't keep me out" line does not work for anyone except a US CBP agent. So basically you need to speak with a CBP agent and without a car you would have to walk to the check point and start explaining. But even they can make your life miserable and send you packing to the nearest Embassy or consulate to arrange a replacement passport before being allowed to enter, if they so decide.

Sneaking across the border or even being outside the country without your passport originally ... well as Forest would say "stupid is as stupid does".

Airlines will not let you board without the proper documentation, ie: passport, period, end of story. The reason being is that public carriers can get fined if you are not eligible to enter the USA and they transport you there.

Trains and buses are also public carriers and are supposed to document that you have permission to cross the border before boarding you.

The "I am a US citizen and you can't keep me out" line does not work for anyone except a US CBP agent. So basically you need to speak with a CBP agent and without a car you would have to walk to the check point and start explaining. But even they can make your life miserable and send you packing to the nearest Embassy or consulate to arrange a replacement passport before being allowed to enter, if they so decide.

Sneaking across the border or even being outside the country without your passport in the first place ... well as Forest would say "stupid is as stupid does".