PA race razor close; Dem Lamb claims win, GOP not conceding

John Henninger, left, and Eric Larson, right, of Cecil Township, Pa., watches early returns at the election night party of Conor Lamb, the Democratic candidate for the special election in Pennsylvania's 18th Congressional District, in Canonsburg, Pa., Tuesday, March 13, 2018.

The Latest: Polls open in western Pennsylvania

Polls are open in western Pennsylvania as voters settle a high profile special congressional race being watched for clues to the upcoming midterm elections. Republican Rick Saccone is trying to stave off an upset by Democrat Conor Lamb in a Pittsburgh-area district that backed President Donald Trump by 20 percentage points in 2016.

Analysis: The math behind Democrats’ quest to win Pennsylvania special election

A volunteer places campaign signs for Republican congressional candidate Rick Saccone outside the VFW Post 4793, March 5, 2018 in Waynesburg, Pa. Saccone is running in a tight race for the vacated seat of Congressman Tim Murphy against Conor Lamb.

In tight Pa. House race, Saccone leans on Trump and his base

Republican Rick Saccone, right, acknowledges the crowd during a campaign rally with President Donald Trump, Saturday, March 10, 2018, in Moon Township, Pa. Saccone is running against Democrat Conor Lamb in a special election being held on March 13 for the Pennsylvania 18th Congressional District vacated by Republican Tim Murphy.

In Pa. union territory, an electoral test of labor’s pull

In this March 6, 2018, photo, Conor Lamb, the Democratic candidate for the March 13 special election in Pennsylvania's 18th Congressional District, greets supporters during a rally at the Carpenter's Training Center in Collier, Pa. less In this March 6, 2018, photo, Conor Lamb, the Democratic candidate for the March 13 special election in Pennsylvania's 18th Congressional District, greets supporters during a rally at the Carpenter's Training ... more In this March 5, 2018, photo, Republican Rick Saccone, right, talks with supporters at a campaign rally in Waynesburg, Pa.