He strongly supported the Andrew Johnson plan of Reconstruction, and by the Legislature that was elected under that plan he was chosen one of the United States Senators, but was not admitted to the seat to which he had been elected.

When the Johnson plan of Reconstruction was repudiated and rejected by the voters of the Northern States, and when what was known as the Congressional Plan of Reconstruction was endorsed and approved, Alcorn decided that further opposition to that plan was useless and unwise, and he publicly advised acceptance of it.

His advice having been rejected by the Democrats, nothing remained for him to do but to join the Republican party, which he did in the early part of 1869.
Since he was known to be a strong, able and influential man,--one who possessed the respect and confidence of the white people of the State regardless of party differences,--he was tendered the Republican nomination for the Governorship at the election that was to be held the latter part of that year.

He accepted the nomination and was duly elected.

He discharged the duties of the office in an able, creditable and satisfactory manner.