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Romney is set address the Hinckley Institute of Politics at the University of Utah later this morning.
"I brought millions of millions people into the Republican Party over the last very short period of time,” Trump said. “It's the biggest story in politics, how many people are flocking into the Republican Party.
“They're leaving the Democrats. They're leaving the independents. They're no longer independent. And they're with me 100 percent.
"There's great enthusiasm in the Republican Party except in the establishment,” Trump argued.