During President Andrew Johnson's impeachment trial, Fowler broke party ranks, along with nine other Republican senators, and voted for acquittal.

Including Fowler, seven Republican senators were disturbed by how the proceedings had been manipulated in order to give a one-sided presentation of the evidence.

The other Republican senators expressing these concerns were William Pitt Fessenden James W. Grimes, John B. Henderson, Lyman Trumbull, Peter G. Van Winkle,[citation needed] and Edmund G. Ross of Kansas, who provided the decisive vote.

[2][3] After the trial, Congressman Benjamin Butler conducted hearings on the widespread reports that Republican senators had been bribed to vote for Johnson's acquittal.

In Butler's hearings, and in subsequent inquiries, there was increasing evidence that some acquittal votes were acquired by promises of patronage jobs and cash.

In 1875, Fowler was selected by the committee planning the public memorial in Nashville that commemorated Andrew Johnson's death to deliver the funeral oration.