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Lamar Alexander (R-Tenn.), who has served in the Senate since 2003, announced Monday that he will not be running for re-election in 2020.
Why it matters: The Tennessee Republican chairs the Senate HELP committee and is considered one of the few members capable of striking deals on health care. This also leaves his Senate seat up for grabs in two years.
Background: Alexander had a tough primary in 2014, per the Washington Post.