"In the very best of years, when you have a unified GOP, Republicans have an electoral disadvantage relative to the Democratic candidate; that's pretty clear," Fratto told CNBC's "Squawk Box."
"Trump is not going to bring unity to the party. If it's a contested convention, and it's someone else, that's not going to resolve unity either. So, [with] a divided GOP and a fairly unified Democratic candidate, I don't think this is a hard question," said Fratto, the former deputy White House press secretary and now managing director at consulting firm Hamilton Place Strategies.
Clinton notched victories in Ohio and Florida on Tuesday, two key swing states. Trump won the Florida GOP primary, but lost in Ohio to the state's governor, John Kasich.
The business mogul might fall short of the majority required, enabling the party's establishment to put forward another name at the July convention in Cleveland to formally pick its candidate.
On Wednesday, Trump warned of riots if he is denied the party's presidential nomination after a string of primary election victories, raising the temperature even more in the heated GOP race.
"If we just look at polls, Cruz is at least running even with Secretary Clinton. That's at least a competitive race. Trump is not running very close at all, but I think the difficulty is what does it look like, whether it's Cruz, Kasich, Trump, after a GOP convention, and what's going to be a contested GOP convention," Fratto said.
According to recent polling data, Cruz and Clinton were in a virtual tie, while Clinton held a sizable lead against Trump.
Florida Gov. Rick Scott, who in the wake of Trump's Florida victory said fellow Republicans should coalesce around the front-runner, told "Squawk Box" he could relate to the real estate tycoon.
"Back in 2010, I was not the establishment candidate. The Republican leaders tried to get me out of the race," he said. If you elect a business outsider person, they can do extremely well, and that's what the voters are seeing this year. We've got to change the status quo."
"I need a partner in Washington that cares about jobs like I do. The Obama administration has not been a good partner for job creation, the most important issue we have in this country."
Since President Barack Obama took office during the Great Recession, the U.S. economy has added millions of jobs and the unemployment rate has fallen to 4.9 percent, its lowest in nearly eight years.
— Reuters contributed to this report.