TL;DR: The 1899 United States Senate election in Pennsylvania was held by the Pennsylvania General Assembly starting on January 17, 1899, to fill the Senate seat occupied by Matthew Quay, the state's Republican political boss. Quay sought election to a third term, but was damaged by an indictment for financial irregularities. Although Republicans had a majority in the legislature, enough were opposed to Quay to deny him re-election. After 79 ballots, the session ended on April 20, the day Quay was acquitted, without the election of a senator. Governor William A. Stone appointed Quay to the seat, but the Senate refused to seat him. Quay blamed his fellow Republican boss, Senator Mark Hanna of Ohio, for this and revenged himself at the 1900 Republican National Convention by backing Thomas C. Platt's scheme to politically sideline Governor Theodore Roosevelt of New York by making him vice president, over Hanna's strong objection.

https://reddit.com/link/10egwsr/video/wfyau7ioumca1/player

Senator Mark Hanna of Ohio, for this and revenged himself at the 1900 Republican National Convention by backing Thomas C. Platt's scheme to politically sideline Governor Theodore Roosevelt of New York by making him vice president, over Hanna's strong objection.