Special election in deep red Pennsylvania district could be bellwether for 2018 midterms Election shaping up to be closer than expected in district Trump won big.

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A special election next month in a Pennsylvania district that went big for President Donald Trump in 2016 could provide early signs of whether Democrats can retake the House in November, or whether Trump supporters can help keep Republicans in power.

The deep-red 18th Congressional District in the southwest corner of the state voted for Trump over his Democratic rival, Hillary Clinton, by double digits in 2016. Now the Trump presidency is motivating both his supporters and his critics in the race to replace former Republican Rep. Tim Murphy, who resigned in October after the Pittsburgh Post-Gazette reported that the congressman, an opponent of abortion rights, asked a woman he had an affair with to get an abortion.

Republican candidate Rick Saccone, a 59-year-old veteran, is facing Democrat Conor Lamb, 33, also a veteran, in the March 13 election.

One Saccone supporter told ABC News’ Dan Harris that she likes the Republican because “he says he was Trump before Trump.”

That is "a good phrase," candidate Saccone told Harris in an interview for “This Week.” "What it means is the issues that President Trump has nationalized, the agenda the people voted in -- cutting taxes, cutting government spending, reducing government regulations that are strangling our businesses, repealing and replacing Obamacare ... Most of those issues I ran on in 2010 in the state House.”

Vice President Mike Pence was in the district that is a mix of suburban and rural areas on Friday to tout his party's candidate, and last month Trump visited the area as well, calling Saccone “a real friend and a spectacular man.”

The Democratic candidate, Lamb, declined to be interviewed by ABC News but told ABC affiliate WTAE in Pittsburgh that he's focusing on reaching voters.

“My strategy is to go straight to the voters and introduce myself and talk to them about the issues that we face here in western Pennsylvania,” Lamb told WTAE. “Not about anyone’s national agenda, but what we need here, and not about the special interests. And that seems to be working so far.”

The race could have national implications.

With at least 41 Republican House members' announcing they are retiring or otherwise not seeking reelection, every seat matters. Democrats need 24 seats to become the majority in the House of Representatives.

In Pennsylvania's 18th District, whoever wins the special election in March will serve only a couple of months before having to run again in May in their party’s respective primary for the 2018 general election and ithen have to win the midterm election in November.

Harris will have much more on this race as part of ABC New’s ‘18 for 18’ midterm coverage, Monday on Nightline.

‘18 For 18’ is ABC News’ powerhouse political coverage of the 2018 midterm elections. To stay up to date, visit ABCNews.com and the ABC News app, and follow our midterm elections alerts.