It's to Romney, according to David Corn:
As Romney campaigns to be CEO of the USA, his conventional GOP opponents—Tim Pawlenty, Haley Barbour, and the others—can be expected to question his claim that he's the best choice to revive the American economy. But they'll be doing so as politicians, without much personal history to back up their charges. Trump, despite a past that includes a string of failed deals (he lost money in the casino business?), will be confronting Romney as a tycoon: businessmano-a-businessmano.
This illuminating quote from Trump on Romney tells the entire story:
Well, Mitt Romney is a basically small business guy, if you really think about it. He was a hedge fund. He was a fund guy. He walked away with some money from a very good company that he didn't create. He worked there. He didn't create… Well, but, look, he would buy companies, he'd close companies, he'd get rid of jobs… I'm a much bigger businessman. I mean, my net worth is many, many, many times Mitt Romney.