How were state's two previous Black senators, Hiram Revels and Blanche K. Bruce elected by legislature? What does that mean?

How the Senate worked before 1913

From 1789 to 1913, U.S. senators were indirectly elected by state legislatures. The voters of a state chose their state legislature, and those legislators then chose who would go to Washington as a senator. The 17th Amendment, ratified in 1913, established the direct election of U.S. senators by the citizens of each state, effectively replacing the previous system. So when Hiram Revels and Bruce went to the Senate, millions of Black Mississippians had no say at all, because they weren't voting for senators, nobody was.

How Hiram Revels got the seat

Hiram Revels was a freeborn man from North Carolina who rose to prominence as a minister in the African Methodist Episcopal Church and then as a Mississippi state senator. In January 1870, Revels presented the opening prayer in the state legislature, and that prayer, described as one of the most impressive and eloquent ever delivered in the Mississippi Senate Chamber, made Revels a United States senator. The legislators who heard it were so moved that they put him forward for the seat. Revels was selected in 1870 to fill the seat vacated by Jefferson Davis, who had left to become president of the defunct Confederacy. Revels made history as the first Black American to be elected to the United States Senate, but he served only 13 months.

How Blanche K. Bruce got the seat

In Bolivar County, Mississippi, Bruce encouraged Black political participation as the county sheriff, tax collector, and superintendent of education, and that local political base catapulted him to a U.S. Senate seat. Five years after Revels, the Mississippi legislature, still under the control of Republicans swept into office as part of post-Civil War Reconstruction, elected Blanche K. Bruce, making him the first Black American elected to a full Senate term. At his swearing-in ceremony, the state's white senior senator refused to accompany his new colleague to the podium.

Why this makes Colom's win different in kind

By forming coalitions with pro-Union white people, Republicans took control of the state legislatures during Reconstruction, and at the time, state legislatures elected the members of the U.S. Senate. During Reconstruction, only the state legislature of Mississippi elected any Black senators. Both Revels and Bruce needed only a majority in that one chamber of lawmakers, not a majority of Mississippi voters.

Colom won a statewide popular election, running in a state that is majority-white, against a sitting incumbent, in a cycle that wasn't supposed to favor Democrats. Revels and Bruce were giants, but they were chosen by legislators. Colom was chosen by the people, and that is a structurally different thing.