Yeah, right...
The Lousiana Purchase was a catastrophic blunder... </sarcasm>
Actually it was blundered into since Jefferson was only attempting to buy New Orleans. Napoleon threw it into his lap when it became clear that the French would not be able to reconquer and hold its New World empire and the British would seize it. He figured better to let them fight the Americans for it.
Jefferson was so oblivious of Napoleon's intentions that he helped him try and defeat the slave rebellion in Haiti.
Napoleon planned to defeat the slaves then move the 20,000 man army to Louisiana. An army far bigger than that of the United States which J had done his best to destroy along with the navy.
Yellow fever and Toussaint put an end to that dream and made Jefferson look like a political genius.
Jefferson's negoitiator was stunned to be offered all of Louisiana and accepted without authority to do so. Fortunately J put his screwed-up understanding of the Constitution aside long enough to buy it. He could not understand that there was sufficient authority to purchase it just from National Security perspectives alone.