Why did the Federalists oppose the Louisiana Purchase?

As seems to happen so often in politics, the Federalists
opposed the Louisiana Purchase not on principled grounds but because they thought it
would hurt them politically.  They claimed to oppose the Purchase because it was
unconstitutional.  But they really opposed it because they thought that the states that
would be made out of the Purchase would be more Democratic-Republican than
Federalist.

In general, the Federalists were an elite party
of New England merchants.  They had some support in other states, but almost solely
among the upper classes.  The Federalists reasoned that the states that were made out of
the Purchase would be settled by small farmers, a class that was solidly in favor of
Jefferson's party.

The Federalists claimed they opposed the
Purchase on constitutional grounds.  They said the Constitution did not give the
president the power to do things like buying territory.  This was somewhat hard to
believe, though, since the Federalists were the party that was in favor of interpreting
the Constitution broadly.  Because their complaints about the Purchase were so contrary
to their usual beliefs, historians believe that their real motive was the fear of losing
political power.