The Democrat understood the district and ran on the issues of that district. Pro gun, pro life (his only position stated was he is personally against abortion), pro tax cut, pro Union, and anti-Pelosi. The Democrat party understood this, stayed out of his way, but sent help and funds trying to create the appearance of a resurgent Democrat Party. Of note, in the previous 2 elections the Democrats never fielded a candidate in this district. In the 2012 election the Dem got 122000 votes, about 10000 more than last night. Hoever in off year elections the rep candidate was getting about 166000. 50000 more than voted last night.
So rather than the Blue Wave the Democrats are trying to create a mythos around, the real story is Republicans stayed home in an election that means nothing. In a few months the district goes away and everything is jumbled due to new lines being drawn.
The Republican was an outlier. Since the district was going away in a few months none of the political class wanted to waste the time and effort it would take to run, only to have to refile and rerun in an entirely new district a week after this election. Saccone, a political novice, stepped up and ran just so the Republicans would have a candidate. His fund raising was abysmal and his initial messaging was incoherent. Up until the last week he had gotten zero support from the national party level. He was running 6-10 points behind until Trump did an appearance last weekend...which bumped the race up to a dead heat.
So, assuming that Lamb (Dem) wins; it is irrelevant to next years election. Sure, the media will try to create the illusion of importance. But they will ignore the fact that their was heavy support from the Democrats (money they really don't have and will need in 5 months) and the Candidate ran against his own Party. His vote tally was about average for a Democrat Candidate with zero indications of any resurgence in the area. And with redistricting in an off-year first term POTUS election, the entire State is probably a crap-shoot at this point (especially since the new district map may again end up in Court and get redrawn yet again).
Never use a small caliber bullet on a large caliber man.