Transcript for Pennsylvania district's special election could be bellwether for 2018 midterm elections
Reporter: Not a huge crowd here, but they've got gusto. Hello, Pennsylvania! Reporter: A rare campaign stop for the vice president. Would you give another round of applause for the next congressman from the commonwealth of Pennsylvania, Rick Saccone. Reporter: Pennsylvania's 18th congressional district has become the latest battleground in America's bitter partisan political fight. They're bringing out the big guns here in southwestern Pennsylvania today for Republican candidate Rick Saccone. Reporter: Rick Saccone, who's 59 and his democratic opponent Conor lamb who's just 33 are facing off in a special election on March 13th for a seat vacated last fall after Republican congressman Tim Murphy resigned amidst a sex scandal. With president trump's approval ratings hovering around 40% -- We need to support the president and Rick Saccone. Reporter: -- Republicans are pulling out all the stops. President trump himself showed twoup weeks ago to support Saccone. A real friend and a spectacular man. Rick Saccone. Reporter: A loss here could signal the start of a potential blue wave backlash against the president. If Saccone wins by single digits, that will be a barometer of the enthusiasm gap for Republicans in districts that have a considerable amount of Democrats who crossed over to vote for trump. Then even though it's a win it still should concern Republicans that in other districts, that that enthusiasm gap is there. Usa! Usa! Reporter: At least in this room, though, there seems to be broad support for trump. Karen Kiefer came with her daughter Tory and her bling. Our vice president and our president are working so hard for we, the forgotten men, women and children in America. The standard of living is improving. New businesses are coming into town. It's marvelous. Reporter: Pennsylvania's 18th congressional district is a mix of suburbs and rural are where trump beat Hillary Clinton by double digits. The district also includes a significant population of union members, a voting bloc that typically goes Democrat. We met three union members on their lunch break, two of whom say they're going Democrat this time. We need somebody out there that's going to represent us, going to make sure they stand for us. Because guess what? We don't have a fight. They've got to fight for us up there. And I believe Conor lamb is the guy that's going to do that. Do you have a candidate you like? Yes. Rick Saccone. I'm a Republican of course. But I think he has the experience. Reporter: When you vote are you voting on local issued or do you have your eye on Donald Trump? My eye's on Donald Trump because I want the country to do good and I think that Donald Trump is a unique president. I think that he's not a Democrat or a Republican. I believe he's an independent. And that's why I like him. Reporter: But if you like him don't you want to send be? From his party up? I'm a renlsed Democrat but whoever I feel best fits the mold. That's why I kind of like Donald Trump. What's interesting about this particular district is that it actually has a 70,000 voter margin for Democrats. And a lot of union members. Almost 80-plus thousand union members. So it's coal country. So a Democrat could potentially upend a Republican there if they have the right message. Reporter: Rick Saccone is a staunch defender of trump's. We caught up with him as traveled between campaign events. You said I was trump before trump. What do you mean by that? The issues president trump has nationalized, attend he voted, in cutting taxes, cutting spending, reducing government regulation that's are strangling our businesses, most of those issues I ran on in the state house. In that sense I say I was trump before trump because I ran on those issues. Reporter: Seize a four term state representative with a wide ranging resume that includes air force counterintelligence unit, North Korea peace negotiator and author of nine books. He says he disagrees bringing in the white house for reinforcement in this campaign is either a sign of vulnerability or liability. They could come here every week and he could fill a stadium. So I want him to come here because I want the people to see their president. Rick Saccone. Thank you. Thank you. Reporter: At an event for young Republicans Saccone doubled down on his support for trump. And he needs help. He needs some wing men down here. I'm an air force guy. I want to go down there and be his wing man. We've got? Air force here. Good. Reporter: Do you think voters in the 18th district are going to look aught and your opponent and judge you on the merits or is this all a referendum on trump? Either way I think I win. So I hope they judge it on the merits of my background and experience and qualifications. But if it's a re6r7bdum ferendum on trump, this is trump country. You just saw it out there. Everywhere I go it's like that. People are for president trump here. He's as popular now as he's ever been. Reporter: But trump is not popular everywhere in this district, and dislike of the plnt has motivated support for Saccone's opponent, Conor lamb. In a Tony suburb of Pittsburgh we attended a meeting where democratic foot soldiers for lamb plotted strategy and then hit the streets. Do you think in part it's fed by the energy out of "Me too" and "Time's up"? I've never done this before in my life. I've always voted. I've never worked for a campaign before. I never protests. I never imagined I'd be protesting on the streets. But I consider it important work for the future of my grandchildren. Reporter: In many ws Donald Trump made you a political activist. Yes. Reporter: Con lamb is a former assistant U.S. Attorney and Marine Corps capital who comes from a political family. This is his first run for public office. He's keeping a much lower profile than Rick Saccone, shunning the national media including our interview requests. He did make his case to our Pittsburgh affiliate this weekend. 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. Not about anyone's national agenda. And that seems to be working so far. He recognizes that the national democratic brand is toxic for him. So keeping it local is what's most advantageous for him. Reporter: National Republicans are pouring in big money to paint conor??lamb as a Nancy Pelosi sock puppet. His name is Conor lamb, but in Washington he'd be one of Nancy Pelosi's sheep. Reporter: This race is just heating up, and the partisan acrimony is only likely to accelerate. In the meantime, though, a lesson for America from those union workers we met outside their factory. Given how differing your views are on trump, can you get along at work? We're all good friends. It doesn't matter? You can't let political things separate you from being a human being. These guys, we've been together, what, 15 years now? 15 years for him. 20 for us. They become part of your family. And guess what. Sometimes with your family -- do you always agree your brothers and your sisters? Reporter: No. No. But you still love them. Reporter: For until in the this is Dan Harris. Thank you, gentlemen. Reporter: In Pennsylvania's 18th congressional district. And a reminder, you can find ABC news's comprehensive "Eighteen for '18" elections coverage at abcnews.com or by downloading the ABC news app and signing up for midterm election Aler alerts.
This transcript has been automatically generated and may not be 100% accurate.