Go ahead, deplore Donald Trump. Despise his message. Reject his appeals to exclusion and hatred. But do not make the mistake of treating him as a solitary phenomenon, a singular celebrity narcissist who has somehow, all alone, brought his party and its politics to the brink of fascism.

He is the leading Republican candidate for president. He has been for months. The things he says are outrageous, by design, but they were not spawned, nor have they flourished, in isolation.

The Republican rivals rushing to distance themselves from his latest inflammatory proposal — a faith-based wall around the country — have been peddling their own nativist policies for months or years. They have been harshening their campaign speeches and immigration proposals in response to the Trump effect. Ted Cruz and Jeb Bush want to allow only Christian refugees from Syria to enter the country, and Mr. Cruz has introduced legislation to allow states to opt out of refugee resettlement.

And party officials around the country, attuned to the power of fear, have developed homegrown versions of the Trump approach. In 31 states, governors — most but not all Republicans — have formed an axis of ignorance, declaring their borders closed to refugees fleeing the Islamic State in Syria. In Texas, Gov. Greg Abbott has sued the federal government and a nonprofit relief agency to keep refugees out. Indiana’s refusal forced one family to seek refuge in Connecticut. Georgia is seeking to deny displaced Syrians federal benefits, like food stamps, and keep their children out of school.