It's being hailed online as the must-see TV event of the summer, and all eyes will be on Donald Trump.
Asked as he was stepping off his private plane in Cleveland whether he prepared for Thursday night's FOX News debate, Trump replied, "Let's put it this way: I've been preparing all my life."
"We have to make our country great again," he added. "That's what we have to do. Make our country great again."
Campaign sources tell NBC News that Trump will do what he does best: be Trump.
Aides have given him detailed policy memos with bullet points -- and he's studying them. But after coming back from Scotland on Saturday, Trump has hardly kept a low profile to prepare.
Since Sunday morning, when he appeared on NBC's "Meet the Press," the billionaire candidate has done at least nine interviews. eight on TV and one by radio, though most were by phone.
On Sunday, Trump downplayed expectations for the debate, telling NBC's Chuck Todd, "I'm not a debater. I've never been on a stage debating...I don't want to be unreal. I want to be me. I have to be me."
While the other candidates have been sparring in mock debates with mock opponents, Trump has been telling anyone who will listen that he's not engrossed in that kind of debate preparation. He's vowed to keep it civil tonight, as long as he isn't attacked first.
Traveling with Trump Thursday night will be his National Political Director Michael Glassner, his South Carolina Director Jim Merrill and his Iowa State Director Chuck Laudner, along with campaign manager Corey Lewandowski and communications leader Hope Hicks.
Trump himself keeps a small inner circle. His closest advisers include his longtime lawyer Michael Cohen and his daughter Ivanka. It's unclear if either will be with him tonight.
Advisers say Trump is sure to talk about his business savvy, his ability to "bring back jobs" abroad, and - perhaps most importantly - immigration.
Aides say that he'll talk about his strategy to build a wall along the U.S. Mexico border. And they say he knows how long, how high, and how much it would cost.