"I think if that happens it would really be the end of the Republican Party. You would have so many disenfranchised and disaffected voters out there that it would just be very, very hard to put it all back together," Levine said Thursday on "The Steve Malzberg Show."
"He by far has the most delegates, yet there are some people in the party, people who I know, good people, who think that he shouldn't get the nomination.
"[They think] for some reason you go to a convention and the delegates … can somehow forget all the people who went to the polls and voted in good faith in order to show their preference…. That's not the way it should be. It should be one in sports on the field and it should be one at the ballot box."
Levine — a deputy New York City mayor under Rudy Giuliani and principal associate deputy attorney general under the Reagan Administration — said he supports Trump and believes the billionaire developer will win the necessary 1,237 delegates to avoid a contested convention.
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And he said he’s optimistic about next Tuesday’s pivotal Indiana primary in which 57 delegates are up for grabs.
"[The Indiana Hoosiers] played in the Pinstripe Bowl in Yankee Stadium … and I got to know a lot of people from Indiana. I've been talking to them and they think that he's going to win it. I've known Donald for many, many years. I think he's very, very competent," Levine said.
"He's a really, really good person and he'll be a great leader. Why am I supporting him? … I think today the country needs an executive. He's an executive. It's about leadership and you can demonstrate leadership by what have you done. He's built a $10 billion business.
"I know a lot of his employees. Employees love him…. You have to be able to compromise to get to where you are. That doesn't mean making bad deals, it means making good deals. He's shown … he can do that."
On Tuesday, Trump got closer to cementing the nomination after a five-state primary sweep, which brings his delegate count to 992, compared to Sen. Ted Cruz’ 562 and Ohio Gov. John Kasich’s 153.
Cruz and Kasich sparked controversy this week when they formed alliance to try to stop Trump in three upcoming primaries, with the Cruz focusing on Indiana and Kasich aiming for Oregon and New Mexico.