After two attempts to resume his place in the Senate, he found that he was unable to remain; yet when his term expired, he was almost unanimously reelected.

Much of his time for three and a half years he spent in Europe.

In December, 1859, he seemed sufficiently recovered to resume senatorial duties, but it was not until the following June that he again addressed the Senate.

On that occasion he delivered his last great philippic against slavery.
The subject under discussion was still the admission of Kansas as a free State, and, as he remarked in his opening sentences, he resumed the discussion precisely where he had left off more than four years before.
Sumner had assumed the task of uttering a final word against slavery as barbarism and a barrier to civilization.

He spoke under the impelling power of a conviction in his God-given mission to utilize a great occasion to the full and for a noble end.