Jefferson to Albert Gallatin 13 jan 1803

there is no constitutional difficulty as to the acquisition of territory, and whether, when acquired, it may be taken into the Union by the Constitution as it now stands, will become a question of expediency. I think it will be safer not to permit the enlargement of the Union but by amendment of the Constitution

https://seaofliberty.org/explore/jefferson-albert-gallatin-quote/258