On Friday, Rep. Conor Lamb made his long-awaited entrance into what was already a crowded Democratic primary for Pennsylvania’s open Senate seat, which will be one of Team Blue’s top pickup targets nationwide next year. Lamb’s decision means that he’s leaving behind his competitive 17th Congressional District in the Pittsburgh suburbs, though no one knows what his constituency will look like once the redistricting process is finished.

Lamb became a national sensation in March of 2018 when he won the special election for a very conservative congressional district that became open the previous year after GOP Rep. Tim Murphy resigned in disgrace in the face of duel sex and bullying scandals. Murphy’s seat, which was numbered the 18th District at the time, had supported Donald Trump by a hefty 58-39 margin in 2016, and few initially gave Team Blue much of a chance to flip it.

Lamb, though, proved to be a very strong candidate for a seat that stretched from the Pittsburgh suburbs into the rural western part of the state. The former federal prosecutor and Marine veteran had deep ties in Western Pennsylvania (his uncle, Michael Lamb, is the city controller for Pittsburgh), and he ran an energetic campaign that brought in plenty of money. The same could not be said for his GOP opponent, state Rep. Rick Saccone, who attracted scorn from his own party for everything from his basic campaign skills to his “porn stache.”

Outside Republican groups ultimately dumped in over $10 million to try to prop up their hapless candidate, and Team Red even sent in Trump himself—twice!—to stump for Saccone, who liked to claim that he “was Trump before Trump was Trump.” None of it worked, though, against Lamb, who campaigned as a moderate. The Democrat ended up beating Saccone 49.8-49.5, an upset that gave Republicans their strongest sign yet just how much the political climate had turned against them. 

The new congressman had to quickly prepare for another contest in the fall, but this time, he didn’t need to run on turf this red. The state Supreme Court had thrown out the GOP’s gerrymandered congressional map earlier that year and drawn a new one after Democratic Gov. Tom Wolf vetoed the Republican legislature’s attempts to pass a new gerrymander. Lamb ended up running in a district, now numbered the 17th District, that was considerably more suburban than the constituency he’d won in March and had backed Trump only 49-47.

Lamb, who worked hard to keep the moderate image he’d cultivated in the special election, faced off against three-term Rep. Keith Rothfus, a Republican who had been an ardent Trump ally. While national observers initially expected a very competitive incumbent vs. incumbent race, though, national Republicans viewed Rothfus as a weak candidate and left him to fend for himself in late September. Lamb ended up beating Rothfus 56-44 in a year where Democrats did exceptionally well in suburban areas like this, and he looked secure going into 2020.

That year, though, proved to be unexpectedly challenging for Lamb. Donald Trump promoted Army veteran Sean Parnell early, and he ended up raising a strong amount of money late in the campaign. The Congressional Leadership Fund began airing ads to help Parnell in the final days of the race, and that investment almost paid off: Lamb fended off Parnell 51-49 as Joe Biden was taking this seat by a slightly larger 51-48 spread.

A number of Republicans, including Parnell, are running to succeed retiring GOP Sen. Pat Toomey, but Lamb has his own primary to get through before he can focus on any of them. The Democratic field already includes two well-funded candidates: Lt. Gov. John Fetterman, who also hails from Western Pennsylvania, and Montgomery County Commission Chair Val Arkoosh, who leads a populous community in the Philadelphia suburbs. A few other Democrats are also in including Malcolm Kenyatta, a Philadelphia-based state representative who would be the nation’s first Black gay senator.

Lamb’s centrist reputation could also prove to be an obstacle in the primary. The congressman notably told the New York Times just after the 2020 election, “I’m giving you an honest account of what I’m hearing from my own constituents, which is that they are extremely frustrated by the message of defunding the police and banning fracking,” a message he argued was both unrealistic and politically harmful. Lamb’s most prominent supporter, Allegheny County Executive Rich Fitzgerald, played up the congressman’s moderate views on Friday, labeling him, “Not too far left, not too far right. Moderate.”

Lamb, though, launched his campaign arguing that he is a mainstream Democrat “somewhere in the middle of where we are as a party.” He declared that he has “economically progressive positions” such as support for unions and campaign finance reform; he also said, “We can achieve very, very progressive results if we’re open-minded about the people we want to elect, and we have a teamwork frame of mind.”