Robert Kagan is a senior fellow at the Brookings Institution and a contributing columnist for The Post.

When the plague descended on Thebes, Oedipus sent his brother-in-law to the Delphic oracle to discover the cause. Little did he realize that the crime for which Thebes was being punished was his own. Today’s Republican Party is our Oedipus. A plague has descended on the party in the form of the most successful demagogue-charlatan in the history of U.S. politics. The party searches desperately for the cause and the remedy without realizing that, like Oedipus, it is the party itself that brought on this plague. The party’s own political crimes are being punished in a bit of cosmic justice fit for a Greek tragedy.

Let’s be clear: Trump is no fluke. Nor is he hijacking the Republican Party or the conservative movement, if there is such a thing. He is, rather, the party’s creation, its Frankenstein’s monster, brought to life by the party, fed by the party and now made strong enough to destroy its maker. Was it not the party’s wild obstructionism — the repeated threats to shut down the government over policy and legislative disagreements, the persistent calls for nullification of Supreme Court decisions, the insistence that compromise was betrayal, the internal coups against party leaders who refused to join the general demolition — that taught Republican voters that government, institutions, political traditions, party leadership and even parties themselves were things to be overthrown, evaded, ignored, insulted, laughed at? Was it not Sen. Ted Cruz (R-Tex.), among others, who set this tone and thereby cleared the way for someone even more irreverent, so that now, in a most unenjoyable irony, Cruz, along with the rest of the party, must fall to the purer version of himself, a less ideologically encumbered anarcho-revolutionary? This would not be the first revolution that devoured itself.

Then there was the party’s accommodation to and exploitation of the bigotry in its ranks. No, the majority of Republicans are not bigots. But they have certainly been enablers. Who began the attack on immigrants — legal and illegal — long before Trump arrived on the scene and made it his premier issue? Who frightened Mitt Romney into selling his soul in 2012, talking of “self-deportation” to get himself right with the party’s anti-immigrant forces? Who opposed any plausible means of dealing with the genuine problem of illegal immigration, forcing Sen. Marco Rubio (R-Fla.) to cower, abandon his principles — and his own immigration legislation — lest he be driven from the presidential race before it had even begun? It was not Trump. It was not even party yahoos. It was Republican Party pundits and intellectuals, trying to harness populist passions and perhaps deal a blow to any legislation for which President Obama might possibly claim even partial credit. What did Trump do but pick up where they left off, tapping the well-primed gusher of popular anger, xenophobia and, yes, bigotry that the party had already unleashed?

Republican presidential candidates fought over immigration reform, health care and peace in the Middle East during the CNN/Telemundo debate in Houston on Feb. 25. (Sarah Parnass/The Washington Post)

Then there was the Obama hatred, a racially tinged derangement syndrome that made any charge plausible and any opposition justified. Has the president done a poor job in many respects? Have his foreign policies, in particular, contributed to the fraying of the liberal world order that the United States created after World War II? Yes, and for these failures he has deserved criticism and principled opposition. But Republican and conservative criticism has taken an unusually dark and paranoid form. Instead of recommending plausible alternative strategies for the crisis in the Middle East, many Republicans have fallen back on mindless Islamophobia, with suspicious intimations about the president’s personal allegiances.

Thus Obama is not only wrong but also anti-American, un-American, non-American, and his policies — though barely distinguishable from those of previous liberal Democrats such as Michael Dukakis or Mario Cuomo — are somehow representative of something subversive. How surprising was it that a man who began his recent political career by questioning Obama’s eligibility for office could leap to the front of the pack, willing and able to communicate with his followers by means of the dog-whistle disdain for “political correctness”?

We are supposed to believe that Trump’s legion of “angry” people are angry about wage stagnation. No, they are angry about all the things Republicans have told them to be angry about these past 7½ years, and it has been Trump’s good fortune to be the guy to sweep them up and become their standard-bearer. He is the Napoleon who has harvested the fruit of the revolution.

There has been much second-guessing lately. Why didn’t party leaders stand up and try to stop Trump earlier, while there was still time? But how could they have? Trump was feeding off forces in the party they had helped nurture and that they hoped to ride into power. Some of those Republican leaders and pundits now calling for a counterrevolution against Trump were not so long ago welcoming his contribution to the debate. The politicians running against him and now facing oblivion were loath to attack him before because they feared alienating his supporters. Instead, they attacked one another, clawing at each other’s faces as they one by one slipped over the cliff. New Jersey Gov. Chris Christie got his last deadly lick in just before he plummeted — at Trump? No, at Rubio. (And now, as his final service to party and nation, he has endorsed Trump.) Jeb Bush spent millions upon millions in his hopeless race, but against whom? Not Trump.

So what to do now? The Republicans’ creation will soon be let loose on the land, leaving to others the job the party failed to carry out. For this former Republican, and perhaps for others, the only choice will be to vote for Hillary Clinton. The party cannot be saved, but the country still can be.

Read more on this topic:

Things got downright personal at the Feb. 25 GOP debate. Here are a few of the most stinging barbs thrown by Donald Trump, Ted Cruz and Marco Rubio. (Peter Stevenson/The Washington Post)

Dana Milbank: Donald Trump is the monster the GOP created

Greg Sargent: The Donald Trump monster is unstoppable

Eugene Robinson: The great fracturing of the Republican Party

E.J. Dionne Jr.: The monumental fall of the Republican Party