Jefferson could easily be considered the most idealistic of what we call the "Founding Fathers" generally those who are most idealistic are those most likely to dispense both beauty in words, philosophy and politics and at some point in their life fail to deliver the goods through their actions either by inaction, failure or hypocrisy. This does not make Jefferson an idiot, in fact you can argue that this process made Jefferson uniquely wise beyond most others. Those that live life with mediocrity including their politics and language are limited in both their ability to inspire and their ability to disappoint thus they are given a lower standard to uphold. Jefferson's words of limited government (gross oversimplification) was challenged by the situation he was put in of incredible power by being President, as all idealists do he succumbed to practicality and chose the security and well being over the country over his principles in his expansion of the government both in military strength and in overall land area control.

In order for me to feel comfortable continuing I would like to know what exactly makes him sound like an idiot in this biography you read.

EDIT: Read "John Adams" by David McCullough