Jefferson's whole political philosophy was based on a radical distrust of central government power and a correspondingly narrow interpretation of that power under the terms of the Constitution. The Louisiana Purchase seemed to go against Jefferson's long-standing republican principles. For one thing, the Constitution did not authorize the federal government to buy property from foreign governments, yet that's precisely what the Purchase involved. Jefferson's Federalist opponents immediately seized on what appeared to be the president's hypocrisy and made an issue out of it.

Jefferson didn't want to be seen as playing fast and loose with the Constitution, but at the same time, he didn't want to lose this once-in-a-lifetime opportunity to expand American territory at what was a fairly reasonable cost. He sent the Louisiana Purchase to the Senate—without amendments—for ratification. Republican control of the Senate ensured that the measure passed comfortably after only a two-day debate—Jefferson's enormous constitutional gamble had paid off.

The purchase to which you are referring is the Louisiana Purchase; this was one of the largest land acquisitions in American history in which Jefferson bought the Louisiana Territory from France. Jefferson had reasons to be concerned, but the deal was too good to let escape. Jefferson's diplomats were only allowed to negotiate for the use of the port of New Orleans—they were not authorized to buy this land. Congress was informed after the fact—all of this is a little ironic since Jefferson is known as a strict constructionist of the Constitution. Also, no one knew the exact parameters of the purchase and some were worried that there would be future land conflicts with Spain and Britain. No one knew what was in the new land either—much of the Louisiana Territory had not seen any white explorers. This intrigued more than worried Jefferson as he sent the Lewis and Clark expedition as a military venture told to also make scientific observations.