This year's last special election left Democrats energized and Republicans worried.

The big picture: A U.S. House race in Ohio that should have been a layup for Republicans instead wound up too close to call with 100% of the vote in, although Republican Troy Balderson and President Trump declared victory.

The AP advisory at 11:25 p.m.: "Republican Troy Balderson has a slight lead over Democrat Danny O'Connor in the special election in [Ohio's] 12th Congressional District. But there are at least 3,367 provisional ballots left to be reviewed. That's enough for O'Connor to potentially pick up enough votes to force a mandatory recount."

"Republican Troy Balderson has a slight lead over Democrat Danny O'Connor in the special election in [Ohio's] 12th Congressional District. But there are at least 3,367 provisional ballots left to be reviewed. That's enough for O'Connor to potentially pick up enough votes to force a mandatory recount." CNN's John King points out that such leads typically stand. But the race is deadlocked for now with a 1,754-vote margin for the GOP.

Why it matters ... Regardless of which way the race tips (in a district that Trump won by 11 points in 2016, and Mitt Romney carried by 10 in 2012), we have learned four things heading into the epic November midterms:

In elections since 2016, Republicans have massively underperformed their Trump-Clinton margins, one of the surest signs of trouble when House control is at stake 90 days from now. MSNBC's Steve Kornacki, after a long night at his "Big Board," told me: "OH-12 was Trump +11 and right now it’s GOP +0.9 in the special. ... PA-18 [went] from Trump +20 to a Dem win" by Conor Lamb. FiveThirtyEight says this year's "federal special elections have shifted leftward from their partisan leans by an average of 16 percentage points." There's a sharp Trump-era shift from the GOP in suburbs, which were a crucial part of the president's 2016 victory. Political analyst Bill Schneider said on CNN that while Trump has a historic hold on his own voters, Republicans are bleeding affluent, educated, suburban voters who don't like him: "It's changing the profile of the Republican Party quite dramatically." Every race is a Trump race. And both sides think that works for them. The president, claiming he saved Balderson's bacon, will be even more insistent about engaging in key races. Axios' Alexi McCammond points out that the Ohio race was really Trump v. Pelosi: The president rallied with Balderson on Saturday; GOP ads tied O’Connor to Dems' Speaker-in-waiting.

Be smart: Both parties will obsess about luring their own people to the polls, with little incentive or bandwidth for outreach to the middle (less likely to vote in midterms than in presidential elections) or the other side (everyone dug in).

That means an ugly, loud spectacle befitting our times.

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