"I do think Donald Trump would be a disaster for the country and a disaster for our party," Paul said on CNN's "Wolf," among several interviews hitting the Republican front-runner.
"I don't think you want a nominee [who] offends whole areas of the public, whole ethnic groups," Paul said, adding that Trump's comments that rapists and other criminals come into the U.S. from Mexico are "crazy talk" and deeply offensive.
"I think most people who immigrated to this country are assets to our community and came here seeking the American dream, the same way my ancestors did," Paul said, dismissing those "painting with a broad brush."
Without referencing his remarks, Trump bashed Paul on Thursday, suggesting the senator should be excluded from CNN's GOP presidential debate this month.
Trump said it was "great" that businesswoman Carly Fiorina, another GOP candidate, was likely in for the Sept. 16 debate, but it could mean a crowded stage.
"I don’t like the fact that there are 11 people now, as I understand it; they’re not getting rid of Rand Paul or somebody, and they should because there’s too many people," Trump said.
"When you have 11, you’re not going to hear me and you’re not going to hear other people talking, and I think that’s too bad," Trump added of the debate, which originally expected 10 candidates.
The suggestion that Paul should be left off the debate stage at the second GOP debate particularly stings with the Kentucky lawmaker, who is floundering in recent polling. 
Paul took to Twitter following Trump's remarks after the businessman signed a pledge ruling out a third-party run:
Paul and other candidates are expected the sign the pledge soon.
"I'll support whoever the nominee is, and I will sign the pledge," Paul said on CNN, adding that if Trump is the nominee, "I think we would suffer the worst defeat since 1964."



 Jonathan Easley contributed