On Tuesday, March 13, Pennsylvania voters will pick a congressman to take the seat vacated by Republican Rep. Tim Murphy, who resigned last year amid scandal.

The two major-party candidates in the special election are Republican state Rep. Rick Saccone and Conor Lamb, a Democratic ex-Marine and federal attorney.

The race has received widespread national attention because of its potential to be a bellwether for 2018 midterm races. Even though President Trump won the 18th congressional district by nearly 20 percentage points in the 2016 presidential election, and a Republican congressman has run unopposed in the last two election cycles, Democratic pick Lamb continually gained ground on Saccone throughout the race.

In fact, on Monday morning, the latest Monmouth poll showed Lamb poised to win the race by margins ranging from two to seven points, depending on various turnout models.

Despite the fact that the district will essentially cease to exist in its current form after the race, due to a redrawing of the state’s heavily gerrymandered map, outside Republican groups have dumped millions into the race in an effort to save face before the midterm elections. Meanwhile, Lamb has largely been able to match those efforts on paid media with his own sizeable fundraising haul.

This congressional race is sure to be a nail biter. Keep an eye on this page for live-streaming coverage of the vote, and live results. Polls close at 8 p.m. ET.