To the Senate of the United States:
I herewith communicate to the Senate, for its consideration, a convention concluded and signed at Berlin on the 29th day of January, 1845, between the United States and Prussia, together with certain other German States, for the mutual extradition of fugitives from justice in certain cases; and I communicate with the convention the correspondence necessary to explain it.
In submitting this convention to the Senate I deem it proper to call their attention to the third article, by which it is stipulated that "none of the contracting parties shall be bound to deliver up its own citizens or subjects under the stipulations of this convention."
No such reservation is to be found in our treaties of extradition with Great Britain and France, the only two nations with whom we have concluded such treaties. These provide for the surrender of all persons who are fugitives from justice, without regard to the country to which they may belong. Under this article, if German subjects of any of the parties to the convention should commit crimes within the United States and fly back to their native country from justice, they would not be surrendered. This is clear in regard to all such Germans as shall not have been naturalized under our laws. But even after naturalization difficult and embarrassing questions might arise between the parties. These German powers, holding the doctrine of perpetual allegiance, might refuse to surrender German naturalized citizens, whilst we must ever maintain the principle that the rights and duties of such citizens are the same as if they had been born in the United States.
I would also observe that the fourth article of the treaty submitted contains a provision not to be found in our conventions with Great Britain and France.
JAMES K. POLK.
James K. Polk, Special Message Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/200664