I believe that Jefferson would have been against annexing Tay-has the way that we did, as he said that his fear was to try and take the lands from the Spanish too soon, as the Spanish were the best people to hold those lands for us until we were ready to annex them piecemeal. Texas almost felt like a honeypot, as the Mexicans lured Whitey in with promises and then used him as an excuse to start a war, leading to us gaining way too much territory too fast. The only saving grace was that we still had some people in power with some sense then, so when the USA wound up conquering effectively all of Mexico as a result of that war, we had the sense to pay Mexico to take it off of our hands. Little did they know that, less than 200 years later, our leaders would let Mexico effectively annex us.