Another day brings another poll with Donald Trump in the lead. According to a new Monmouth University poll of Republicans nationwide released Thursday, the real estate mogul leads the pack with 30 percent of the vote. His next closest competitor, retired neurosurgeon Ben Carson, takes 18 percent. By contrast, the most mainstream and viable candidates—Jeb Bush, Sen. Marco Rubio, and Govs. Scott Walker, John Kasich, and Chris Christie—take 8 percent, 5 percent, 3 percent, 2 percent, and 2 percent respectively, for a combined total of 20 percent support between the five of them.

In other words, the age of Trump is here, it shows no sign of retreat, and Republican leaders are nervous. If Trump becomes the nominee—still unlikely, for the same reasons it’s difficult for Sen. Bernie Sanders to pull a win in the Democratic primary—he’d be an easy target for Democrats, who could blast him for everything from inexperience and temperament, to his nativist rhetoric and unsubtle racism. But a Trump nomination is so unlikely that it’s not the actual nightmare for the Republican Party. The nightmare is a third-party run, where Trump gets himself on the ballot in all 50 states, and siphons white voters from a GOP that needs white turnout to win national elections.

That nightmare is why, on Wednesday, the Republican National Committee privately circulated a “loyalty pledge” to the party’s presidential candidates. “I [name] affirm that if I do not win the 2016 Republican nomination for president of the United States I will endorse the 2016 Republican presidential nominee regardless of who it is,” reads the pledge. “I further pledge that I will not seek to run as an independent or write-in candidate nor will I seek or accept the nomination for president of any other party.” The obvious hope was that Trump would agree, rule out an independent run, and let Republican leaders breathe easy (or at least, more easily).