If you leave US mainland customs zone and go to saipan or Guam or something it will probably slow you down and they might claim you need it, even though you don't. Also Mexico never changed their law like US did, iirc you can still enter Mexico with a birth certificate.
If you're near a port of entry, you actually can be stopped at any time to be asked for proof of citizenship/visa/etc. See also https://www.aclu.org/know-your-rights/border-zone There are plenty of border patrol stops along highways that never cross a border where you'll be routinely stopped.
In practice, that means "near the border with Mexico" where there are border patrol stations along highways well inside the US that do routine stops, but technically it applies to any port city as well.
_Technically_, if you're a US citizen, you're not required to have proof of citizenship on you. But a drivers license in the US does not show that you are a citizen, and they absolutely can stop you from leaving (at least long enough to mess up your day plans) if you cannot actually prove citizenship in practice. It's just a _lot_ easier to have a passport on you. Passport cards exist mostly for this purpose.
E.g. I lived in Texas for a long time and have a passport card for that specific reason. Driving down to the beach or just going on random trips involves passing through border control stations even though you never leave the US or even get particularly near the border. Your chances of just going to visit a friend in south Texas and winding up needing to pass through a border control checkpoint due to unplanned road closures/etc are pretty high, so it's best to have a card in your wallet at all times that counts. Most remote highways have them as soon as you get back near a town. Most of the time, they'll wave you through pretty quickly, but it's just a lot faster process if you have a passport card and not only a drivers license.
Side note: A friend of mine was a park ranger at Carlsbad Caverns. He picked me up at the El Paso airport and we were driving to Carlsbad. We went through a border control checkpoint. They threatened to arrest him on the spot because he had his park service uniform hanging up in the back, but no employee ID or other proof that he actually was a ranger. They said he was impersonating a federal officer. They made a big deal of it and made us wait while they called the park to verify he was employed (and that didn't work because it was about 8pm). We eventually got let go with a warning after he found random online photos of him giving cave tours and convinced them that he couldn't possibly have staged a ton of random folks on the internet to have him in the background of photos.... But still, it was kinda nuts...
I think people often think something they did or didn't do lead them to be fucked with. Having gone through the border and checkpoint many many times with absolutely wild variation despite doing same stuff, my observation it is 99% whether the officer is bored or sadistic and 1% the totality of the situation.
Slight correction: "enhanced" driver licenses are citizen-only, and this is actually checked during issue, so they can also serve as proof of citizenship.
To clarify some of the confusion in this thread, a REAL ID driver's license is completely different from an enhanced driver's license. A REAL ID meets federal security standards and is available in all states. An enhanced driver's license proves U.S. citizenship and includes RFID but is only available in five states.
Enhanced driver licenses, not regular ones. These come with a whole lot of federal strings attached, and exist pretty much entirely for the purpose of traveling across the border without a passport. As far as I know, the feds require citizenship checks for any participating state.
Now, in some states, regular driver licenses have a citizen or non-citizen marker on them, but that's a whole separate thing (and AFAIK the feds don't consider them sufficient proof in any case).
I have a US passport. I use it when I go to another country.
When I have traveling within the US I never take my passport. There is zero need and I may lose it so why even bother taking it when it serves no use?
My trip was a 6 week long road trip from the south eastern US through Texas, New Mexico, Arizona, California, up to Seattle in the northwest, and then back to the south eastern US.
I had no intention of going to Mexico or Canada. They are fine countries but that was no the intent of this trip so I left my passport at home.
During this trip I learned that the US border patrol has set up border inspection points about 10 to 50 miles inside the US. Most of the southern border are remote desert regions where people can cross on foot and then try to meet up with someone in a vehicle on the other side. So the border patrol doesn't just patrol the actual border but has checkpoints inside the US on the roads near the border.
You don't need a passport to get through these as you never left the country.
But I was driving a vehicle (Honda CR-V) with an open cargo area that showed it was full of luggage, bags of food, and lots of water bottles. I probably looked suspicious like I was picking up immigrants on foot or smuggling drugs.
I wasn't. I was on a big road trip and wanted to be prepared for days if my car broke down on a side road and I was stuck in a desert area waiting 3 days to be rescued.
EU citizens don't need a passport to travel across the EU (even outside the Schengen area, where you have to go through a border check), they just need an identity card.
(most) EU citizens could also travel to Turkey with their identity card.
EU citizens could travel to the UK with their identity card, for a few years after Brexit, as long as they got UK (pre-)settled status.
Russian citizens can travel to Armenia, Belarus, Kazakhstan, and Kyrgyzstan without their international passport. They instead have an "internal" passport (meant to be used like an identity card, and for travel to closed towns inside the country), which is recognised by those other countries.
The same applies in the other direction for citizens of nearby countries travelling to Russia (even in the case of an Abkhazian internal passport. Abkhazia is recognised by only ~6 other UN member states).
I'm not sure in which way a US "passport card" differs from a plastic identity card. But it's notable that a few countries don't have either (UK doesn't... Russia and a few neighbouring countries, as mentioned before, instead have an "internal passport")
Of course, something in common with all the examples above, and with US citizens travelling to Mexico, is that you're travelling to neighbouring countries with friendly relations.
To add to that: in virtually every country in South America their citizens can visit the other countries in South America with only an ID card, no passport necessary.
> Of course, something in common with all the examples above, and with US citizens travelling to Mexico, is that you're travelling to neighbouring countries with friendly relations.
Militarily speaking, yes. But unlike the other examples, there is a huge economic difference between the US and Mexico, meaning migration flows exclusively one way. Illegal crossings are extremely common and the US has strong incentives to prevent them. It's hard to compare the US-Mexico border to any other border in the world.
> I'm not sure in which way a US "passport card" differs from a plastic identity card. But it's notable that a few countries don't have either (UK doesn't... Russia and a few neighbouring countries, as mentioned before, instead have an "internal passport")
US simply doesn't have any official identity card.
So they make up replacements for when it's convenient to actually have one.
I suppose the goal is to encourage innovation in the identity theft industry... after all it adds to the PIB doesn't it?
Circa 2018, I was travelling from Greece to Germany. For whatever reason, the Bundespolizie decided to check everyone’s passports. In particular everyone from Ireland was demanded to have a passport - their identity card wasn’t good enough.
They were on a road trip in the United States and never crossed an international border. Why would they need a passport? I've never taken mine on a trip like that.
Funny, since half of U.S. citizens don't have a passport.