Having assisted a relative on a political campaign in Texas, I do know how the system works:
1) Most voter registration is PUBLIC RECORDS, but only some is on the web. Specifically, you can use the web to verify if a person is registered to vote, by knowing name and birth date.
2) In Texas, when you register, you do not declare a political party. But if you vote in a Primary, you have to pick a party first, and that is recorded (not who you vote for, but which party’s primary did you vote for, if any). And it is a PUBLIC RECORD. Just fill in his name and birth date here (birth date is July 27, 1998):
https://apps.collincountytx.gov/VoterRegistrationSearch/Home/Search
3) However, the party you vote for, while a public record, is NOT on the web. If people want that information, they need to go to the county clerk’s office. In this case, it’s Collin County, outside of Dallas, and buy a voter list, which are sold by precincts (not too expensive for the smaller lists). They may ask you why you need it, and they will remind you that it’s illegal to use that information for commercial/marketing purposes. The reason they let you buy it is so that you can find out which voters are more likely to support you, and which ones not to waste your time with, if you’re a candidate or helping a candidate. For Collin County, the County Seat is McKinney, so you’d go to the County Building there to obtain the list.
4) If I were doing that, I’d say that I was working for his state representative (Jeff Leach) and buy the information covering his district, although they’d probably sell it to me if I were in the media. You could try just asking for his information, but it all depends who you run into there.
5) That list would have his voting record for the past 3 years. It still won’t say flat-out if he’s Democrat or Republican, but it will say which, if any, primaries he voted in.
I live too far to do that, but if I did live in the Dallas area, I would be there first thing tomorrow, although I’d probably not be alone waiting for them to open.