Tell that to all the people that don't want the government keeping track of them with their ID laws. Just because someone is a citizen of the United States doesn't mean the US can demand that they carry a government provided ID. Smaller government, remember?
Keeping track of them? Your SSN can be tracked, your DL can be tracked. We have a fragmented system. It's not impossible to track you. If there was a manhunt, believe me, the federal government will have your cell phone records, cell phone location, CC records, bills, SSN, DL, any form of ID pulled up and everything you could possibly imagine.
If the government wanted to it could. A national ID isn't really about tracking you. There are many other forms of government documentation that already is linked to the majority of Americans that can be used as tracking (tax documents, SSN, passport, drivers license).
You could make it nearly anonymous too such as swiping your ID, and it checks the hash of your name against a database of hashes. It's just to check that you voted once and you're a legit person. Kinda like passwords you know? Hash checks.
I'd like to have some basic ID laws to make sure you prevent ID and that there's a reliable system to count that you've voted once and only once.