Just a few months after Barack Obama was inaugurated in 2009, at a Tea Party march on the National Mall, the signs participants carried portended the escalating, toxic antipathy toward a black president who many on the far right believed to be a secret, un-American Muslim. "Obamaism is an assault on America," read one sign. Another called the president an "undocumented worker." One bore an image of a devil-horned Obama, with the words, "America's Biggest Man-Made Disaster: Barack Hussein Obama."

Those ideas still fester on the far right. Indeed, Donald Trump's vitriolic, anti-Muslim campaign is the product, not the source, of a significant segment of the Republican electorate's irrational fear and loathing of outsiders and immigrants, particularly Muslims. Trump knew this long before he ran for president this cycle. But it took a perfect storm of circumstances for him to fully capitalize on it: the rise of ISIS, the San Bernardino shootings, and a cowardly Republican Party too fearful of Trump's base — in fact, their base — to condemn his vitriol.

Trump voters, enraged by a supposed tyrant, are now supporting a candidate who has unabashedly promised to rule as one. The only cure for the tyrant Obama — an oppressor motivated, they believe, by an un-American religion — is the "tell-it-like-it-is" Trump. The cure for Obama the infiltrator is a President Trump who will ban the Muslims and muse about how brave it would be to execute them with bullets drenched in pigs' blood.

Trump's anti-Muslim presidential campaign was years in the making. During the Obama presidency, Republican lawmakers held hearings portraying American Muslims as clandestine radicals or clueless dupes in the grip of would-be terrorists. Bryan Fischer, a leading radio talk show host and activist, said Muslims are a "toxic cancer" who worship a "demon God" and that they should be banned from entering the country or deported if they are already here. During the 2012 presidential race, Republican candidates appeared on his radio program, as have other Republican lawmakers. At conservative gatherings it was not at all unusual to hear statements like "Islam is not a religion," or worse. Republican lawmakers in several states attempted to ban Sharia law.

By the time Trump launched his campaign in 2015, the Cassandras of a Muslim invasion of America on talk radio, Fox News, and elsewhere had laid his groundwork. Trump sought to exploit the simmering Islamophobia in a series of attention-grabbing moves. In April 2011, during a period when Trump was sending his own investigators to Hawaii to find Obama's birth certificate, he told the Christian Broadcasting Network that the Koran "teaches some very negative vibe."

It would take four more years, during which Islamophobia was on the rise, for Trump to make full political hay of his twinned anti-Obama and anti-Muslim strategy.

In November of last year, a poll found an increase in anti-Muslim sentiment among Americans, particularly white Christians. Compared to 2011, more Americans were agreeing with the statement that Islam "is at odds with American values and way of life." Around the time this poll was released, Trump was calling for the surveillance of mosques and considering closing them. The reaction — that is, the lack of reaction — to Trump's proposal demonstrates just how uncontroversial it was to so many Republican voters.

By the time Trump called for a "total ban" of Muslims from the United States a few weeks later, in early December, the Republican Party had already been cowed into a corner by its dual fears: first, of Muslims, and second, of crossing Trump. Republican mega-donors are reluctant to spend money going after Trump "partly because they are scared of incurring Trump's wrath," according to Politico.

The Republican Party leadership may now be wringing its hands about a Trump nomination, but when it comes to Islamophobia, it has done little to rein in the outright bigotry that has migrated from the fever swamps to the party's presidential frontrunner. His rivals, in barely contesting Trump’s fitness to be president, have done little more than meekly differ with him.

Republicans spent the last eight years terrifying people about Obama undermining democracy and religious freedom. Now the GOP base is convinced that the only solution is to elect a president who really will undermine democracy and religious freedom.