[3] Due to his success in the treaty negotiations, he received an appointment as ambassador to France in 1872, a post of great difficulty and responsibility.

He was looked upon by the Conservative Party, which were trying to overthrow Bismarck, as his successor, and it is said that he was closely connected with the court intrigues against the Chancellor.

A Vienna newspaper published some correspondence on the Vatican Council, including confidential dispatches of Arnim, with the object of showing that he had demonstrated greater foresight than Bismarck.

That recourse to the criminal law against a man of his rank, who had held one of the most important diplomatic posts, caused great astonishment.

In 1875, he anonymously published the pamphlet "Pro nihilo" in Zurich, in which he attempted to show that the attack on him had been caused by Bismarck's personal jealousy.

He made repeated attempts, which were supported by his family, to be allowed to return to Germany to take his trial afresh on the charge of treason.