Why was the Louisiana Purchase both a great opportunity and a signific

Why was the Louisiana Purchase both a great opportunity and a significant problem for Thomas Jefferson?

What will be an ideal response?

ANSWER
Opportunity: doubled the size of the United States; assured control of the Mississippi River and port of New Orleans; ended the threat of a powerful French presence on U.S. borders.
Problem: costly purchase, there was no constitutional provision for purchase of foreign territory (it required use of implied powers).