In what ubiquitously has been referred to as a stunning upset, House Majority Leader Eric Cantor lost his Virginia primary race against a tea party-backed professor. And with that, the second-highest ranking Republican in the House effectively lost his seat. While still a congressman until next year, he has announced that he is stepping down from his leadership position.

There are a number of reasons for Cantor’s loss, not the least of which is that in his quest for a national leadership role he reportedly has paid too little attention to his district. All politics, after all, is local.

At the same time, the larger lesson has to be one best expressed in an old limerick:

“There was a young lady of Niger

“who smiled as she rode on a tiger;

“they came back from the ride

“with the lady inside,

“and the smile on the face of the tiger.”

Cantor, like too many Republicans, had tried to harness the energy of tea party radicals to advance his agenda. Whether that was a cynical political calculation or an honest error in thinking that the tea party movement is an extension of true conservatism is hard to know. That it was wrong, however, is clear.

The wrath of the tea party movement always has been directed more at Republicans than Democrats. Its principal targets are what the zealots call RINOs – Republicans in name only ­– and its weapon of choice has been the primary.

That works in part because most states allow only voters affiliated with a party to vote in primaries and in part because most voters pay too little attention to primary elections. A focused and energized cadre of like-minded voters therefore can have a hugely disproportionate effect on the outcome of an election. Only 65,000 votes were cast in Cantor’s Richmond-area primary. That was up significantly from his last primary, but with around 700,000 people in a typical congressional district, 65,000 is a manageable number for a targeted insurgency.

What all this will mean, of course, is up for discussion. The tea party movement already has succeeded in pulling the GOP to the right. And with Cantor’s defeat at the hands of a man who made opposition to “amnesty” his No. 1 talking point, the immediate speculation was that any chance of immigration reform is dead.

With that, Democrats think the Republicans will further alienate the country’s fastest growing demographic. And if they are right, the tea party may have handed the Dems a generation-long lock on the White House, and maybe the Supreme Court.

If that analysis is correct, the GOP will have brought it on itself by trying to co-op the crazies. The tea party’s agenda is not that of the Republican Party. It is reactionary and focused on ideological purity. And to the extent that it succeeds in pulling the GOP away from mainstream America, it threatens our democracy. We need two parties governing, not one running the country and another howling at the moon.