The March 13 special election in Pennsylvania’s 18th Congressional District will be the first big race of 2018, providing a pulse check for Democrats as they head into the midterms anxious to flip control of the House.

Democrats like their candidate. Conor Lamb is a 33-year-old Marine veteran and former assistant U.S. attorney running for the open seat. But strategists are cautious because President Trump won the district by 20 points in 2016.

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