CANONSBURG, PA - MARCH 14: Conor Lamb, Democratic congressional candidate for Pennsylvania's 18th district, speaks to supporters at an election night rally March 14, 2018 in Canonsburg, Pennsylvania. Lamb claimed victory against Republican candidate Rick Saccone, but many news outlets report the race as too close to call. (Photo by Drew Angerer/Getty Images)
Pennsylvania election shakes up 2018 races
01:28 - Source: CNN
CNN  — 

Nearly one month after his upset victory in Pennsylvania’s 18th District special election, Democrat Conor Lamb was sworn into the House of Representatives on Thursday evening by outgoing Speaker Paul Ryan.

Lamb will serve out the remaining eight months of former Republican Rep. Tim Murphy’s term.

Lamb was the first, and so far only, Democrat to flip a House seat out of the seven special elections held during Donald Trump’s presidency. There are two more special elections scheduled between now and November.

“We are all in this together, we need solidarity with each other,” Lamb said during his first remarks on the House floor, in a call for more bipartisanship.

Lamb’s March 13 victory helped boost Democratic enthusiasm and optimism heading into the stretch through November. Democrats now need a net gain of 23 seats in the fall midterms to take back the House.

During last month’s election, Lamb beat Republican state Sen. Rick Saccone by just 755 votes – a major upset in a district Trump won by 20 points in 2016.

RELATED: 7 takeaways from Conor Lamb’s huge but very close night in Pennsylvania

The district was previously considered so safe for Republicans that Democrats did not even have a candidate against Murphy on the ballot in 2014 and 2016.

The seat opened after Murphy resigned from the House last October. The resignation followed reports that Murphy – who compiled a staunchly anti-abortion rights voting record in Congress – tried to privately convince a woman he had an extramarital affair with to have an abortion, according to messages obtained by the Pittsburgh Post-Gazette.

Outside spending

The special election drew national attention and major investments from top outside groups involved in the race for control of the House.

Republican outside groups spent more than $10 million in an unsuccessful attempt to rescue Saccone, who many operatives believe ran a lackluster campaign. Democratic outside groups spent about $2.5 million on the race.

During the months and weeks leading up to the election, top surrogates on both sides of aisle flocked to campaign in the Pittsburgh-area district to stump for their candidate, including Trump, Vice President Mike Pence and former Vice President Joe Biden.

Two winners in the end?

It’s not over yet for Saccone.

Despite the intensity and expense to both sides, the district will disappear in January. The state Supreme Court redrew Pennsylvania’s congressional map after a long-fought gerrymandering case earlier this year.

Lamb is now running in an incumbent-vs-incumbent race against GOP Rep. Keith Rothfus in the new, more-Democratic friendly 17th district, while Saccone is running in the new, more Republican-friendly 14th district.

So, less than one year after his bruising defeat, Saccone could still end up in Congress alongside his former opponent.