Now, to the cliffhanger in Pennsylvania. 24 hours later, the race still too close to call, but Democrat con Conor lamb has declared victory. In a congressional district president trump won by nearly 20 points. What could this mean for November? ABC's chief national correspondent Tom llamas is there tonight. Please welcome to the stage congressman-elect Conor lamb. Reporter: Tonight, the Democrats proclaiming victory. It look a little longer than we thought, but we did it. Reporter: Democrat Conor lamb holding onto a slim lead over Republican Rick Saccone in a special election for a house seat held by Republicans for 15 years. And where trump won by nearly 20 points just over a year ago. Reporter: President trump flying here three days before the election to rally the base. We need him. We need Republicans. We need the votes. Reporter: Even though it appears Republican Rick Saccone is unlikely to catch his opponent, he insists it's not over. We're going to fight all the way to the end. You know I never give up. Reporter: Republican leaders nationally quick to point out that the Democrat ran on an exceptionally conservative platform. Both of these candidates, the Republican and the Democrat ran as conservatives. Ran as pro-gun, pro-life, ant anti-nancy Pelosi conservatives. Reporter: And regardless of the final outcome, Democrats say their success here is proof momentum is in their favor heading into the midterms. Tom llamas up all night with this. He joins us live from Carnegie, Pennsylvania, tonight. They're still counting provisi provisional ballots, but what's the math here? Is there any way for the Republican to come from behind here and pull this out? Reporter: Well, David, we think there are hundreds of provisional ballots still out there, but there would need to be more than 627 of them, and the Republican would have to win them all. That's highly unlikely. It's looking more and more like this is Conor lamb's race to win. David? Tom, thank you. And one more headline out of