Right now, you're able to select the appropriate gender marker on your passport without a note from a medical professional (and a passport can be used in the vast majority of situations you'd use a birth certificate) but because the self select gender marker was done by executive action, it's extremely likely to be reversed when Trump takes office.
Another tip: A passport card is considered as valid as a passport book within the US, but it is much cheaper to obtain. It is conclusive proof of citizenship and an authoritative RealID-compliant identity card, just like a passport book. Passport cards are valid for land and sea travel within North America and the Caribbean. They're not valid for international air travel (but they can be used for domestic flights).
Edit: Upgrading from a passport card to a passport book is considered a renewal rather than a new application. You can still keep the card if you later want to "renew" it for a book.
This sounds like exactly the type of thing they'll reverse, either through executive action or pushing through the GOP Congress and Supreme Court. If you can afford it, go for the full US passport.
Honestly, I doubt they'd mess with the cards. They're extremely common and useful for people who live in border states - Minnesota encourages them at our DMVs, and if you know about the northwest angle it's likely a big part of why.
What incentive would they have to tamper with passport cards? They're pretty popular in the border regions as an inexpensive way to get an international travel document.
They are also mentioned in several international treaties, particularly with Canada and Mexico. The president doesn't have the power to unilaterally abrogate those treaties.
I'm rushing to get my name legally changed so my updated passport can be correct. My current one has 5 more years, but so it's all my amab info. I'm terrified of how little time is left.
Are they likely to reverse changes once they are made? Say I get my passport application/order in before he takes office. Is it still likely to go through?
IIRC it's a lot harder (legally and practically, because figuring out which applicants are transgender requires sifting through paperwork) for them to invalidate passports that have already been issued. I got my first passport before the first Trump term with my correct name and gender on it and had no issues, but all the paperwork went through during the last days of the Obama admin. I do remember hearing about people having trouble getting the right passport after he came into office. So if you want it and can afford to pay to rush it, it's not a bad idea.
Edit: I would say that probably the people most in danger of having their passports invalidated soon after he takes office are people with X for their gender marker. That would be much more simple than invalidating every trans person's passport that has an M or F on it.
That's good to know. I'm definitely gonna rush to get all of my docs changed after I get my certificate of name change in the mail. Unfortunately can't get my birth certificate changed because of the state I was born in.
Get a passport card. It is legally the same as a passport book within the US (it can also be used for international land and sea travel within North America). It's only $30 to apply and a $35 issuance fee. $65 in total for a piece of RealID-compliant identification valid worldwide for ten years.