Pat Toomey, a moderate Republican senator from Pennsylvania, is set to retire at the end of his term in 2023. This will leave the Senate with only a handful of moderate Republicans, a group that has dwindled in recent years. Toomey has been seen as a voice of reason in the Senate, willing to work with Democrats on issues such as gun control and climate change. His retirement is likely to further polarize the Senate and make bipartisan cooperation even more difficult.