According to the Lincoln Institute, Fessenden "... was chairman of Senate Finance Committee, which had responsibility for raising funds for the Civil War. He held that position before he succeeded Salmon Chase as Secretary of the Treasury on July 1,1864 and returned to it eight months later...
"Quick action was needed to replace Chase in July 1864 and Lincoln's first choice from Ohio wisely declined the nomination. Ohio Governor John Brough met with President Lincoln the night of the Chase resignation and was told by President Lincoln that 'this is the third time he has thrown this resignation at me, and I do not think I am called on to continue to beg him to take it back, especially when the country would not go to destruction in consequence.' Over the next two days, Brough met several times with President Lincoln and finally urged him to appoint Fessenden. 'He will not accept,' said the President, to which Brough responded: 'The public will compel him to.'
"Fessenden himself did seek to turn down the appointment but the President persuaded him to accept -- and had the Senate confirm him while Fessenden was still at the White House. Lincoln valued his prickly integrity and told Fessenden: 'Fessenden, the Lord has not deserted me thus far, and He is not going to now --you must accept!'
"Fessenden served until March 1865 when he returned to Senate (rather than allow outgoing Vice President Hannibal Hamlin to get the seat)... Upon his return to Congress, Fessenden became chairman of Joint Committee on Reconstruction. He was one of a handful of Republicans who voted against removal of President Andrew Johnson, thus earning him the enmity of Radical Republicans with whom he had once been identified."