Washington (CNN) Democrat Conor Lamb appeared to eke out a massive -- and massively important -- special election victory over state Republican Rep. Rick Saccone to claim a southwestern Pennsylvania congressional district that Donald Trump won by 20 points in 2016.

Lamb's apparent win -- no matter how narrow -- will surely rock the national political landscape. Republicans, already jittery about their chances of holding the House in November, will be thrown into panic by this result. And Democrats, already energized by the prospect of sending a message to President Trump, will be further convinced that November is going to be very, very good for them.

Here are seven takeaways from Tuesday's vote in Pennsylvania:

1. The national environment is WAY tilted toward Democrats

This district is nothing close to neutral ground for the two parties. This is a seat Republicans win in anything but a truly terrible national environment. (Remember that Republican Rep. Tim Murphy, who resigned amid a sex scandal late last year, didn't even have a Democratic challenger in 2014 or 2016.) There are dozens of seats currently held by Republicans that are less friendly for their side than Pennsylvania's 18th. If all of those seats are made competitive by Trump's unpopularity -- and the energy of the Democratic base -- then we are looking at the possibility at least of a very large Democratic wave building in advance of the November vote.

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