Eric Cantor's shocking defeat at the hands of David Brat is that rarest of things in American politics: a genuine earthquake. And like with real earthquakes, the damage will be much greater because so few were prepared. A few provisional thoughts:

The Republican Party's core problem isn't the extremism of its members but the weakness of its leadership. Tonight, the Republican Party's problem got much, much worse. "Republicans" are not the same as "Republican primary voters." In 2012, Eric Cantor won the general election with more than 220,000 votes. Tonight, Brat beat him with about 36,000 votes. It's possible and even likely that the vast majority of Republicans in Virginia's 7th District liked Cantor just fine. But primaries only count the people who come out to vote. Immigration reform is dead and Hillary Clinton's presidential hopes are so, so alive. Mere weeks ago the press was writing the Tea Party's obituary. Tonight, the Tea Party claimed its single biggest scalp. This speaks to the weird way the Tea Party exerts powers. The power of the Tea Party has never been the number of Republicans it defeated in primaries. The overwhelming majority of Republican incumbents running for reelection win their primaries without trouble. Rather, it's been the prominence of the Republicans the Tea Party defeated that give the movement its sway. Dick Lugar, Mike Castle, and Bob Bennett. They were institutions. And Eric Cantor's loss is a nearly unprecedented event in American politics. These losses mean no Republican is safe. And that means that as rare as successful Tea Party challenges are, every elected Republican needs to guard against them. The Republican Party has a serious data problem. In 2012, Mitt Romney's internal polls were garbage. This year, Eric Cantor's internal polls showed him up by more than 30 points. Something is deeply wrong with the GOP's campaign infrastructure if the party's presidential nominee and the party's House majority leader can't rely on their pollsters. "A Cantor loss will send a chill down the spine of so many House GOPers contemplating compromise," tweeted my old colleague and friend Zachary Goldfarb. "A disaster for Obama." That seems...wrong. House GOPers weren't seriously contemplating compromise before Cantor's loss and they're not contemplating it after his loss. In terms of legislative achievements, Obama's second term has been done for some time. But in terms of protecting his legislative achievements — and protecting coming executive branch actions like his proposed climate rules — what matters most for Obama is that a Democrat wins the presidency in 2016. Tonight made that a little more likely. Some on the left are envious of the Tea Party's success at cowing Republicans. "The Left endorsed Cuomo; the Right successfully primaried the sitting House Majority Leader = how the country keeps moving to the right," tweeted Max Berger. Others voiced similar sentiments. But this isn't how the country keeps moving right. This is how the country keeps moving left. If Republicans hadn't scared Senator Arlen Specter into the Democratic Party and if Democrats hadn't kept Senator Joe Lieberman on their side Obamacare would never have passed. If the Tea Party didn't keep knocking off viable Republicans Mitch McConnell would have been Senate Majority Leader since 2010. If Mitt Romney could have run as the Massachusetts moderate he once was Obama might well have lost in 2012. It's possible Republicans will now lose in Virginia's 7th District. The Tea Party is good at policing purity but they're terrible at winning power. Of late, there's been a lot of talk about "reform conservatism," a gentler, more inclusive, more wonkish brand of conservatism. Cantor, a founding member of the "Young Guns," was one of reform conservatism's patron saints. His loss suggests reform conservatism doesn't have much of a constituency, even among Republican primary voters. The Republican base, at least in Cantor's district, isn't in the mood for technocratic solutionism. It's still angry, and it still believes that any accommodation is too much accommodation. John Boehner must be having an emotionally complicated evening.

Further reading: For more on Eric Cantor's shocking loss, see the full storystream here.