Jimmy Vaccaro has run sports betting in various casinos in Las Vegas for 40 years now. He could quickly calculate the spread for next year’s opening football weekend in his head, but it wasn’t until last summer that he began to get interested in the Super Bowl of politics — the presidential election....

In August, that began to change. Customers came up to the gleaming sports book counter at South Point Casino and asked if they could place their money on real estate tycoon Donald Trump instead of the Giants. Vaccaro didn’t like turning them away, so he began releasing weekly odds sheets, calculating each candidate’s chances to win the Democratic and Republican presidential nominations. The sheet is emblazoned with the words, “FOR ENTERTAINMENT PURPOSES ONLY,” since political betting is for the most part outlawed in the United States.

Bettors at South Point, a working class casino a few miles from the strip that is filled with locals and some vacationers, would take the sheets and begin arguing about their favorites....

They’re also Donald Trump’s base. The Republican frontrunner held a rally at the casino last month, which quickly reached capacity. The overflow filled the hundreds of chairs in the sports book section, and Vaccaro realized this election was going to be different.