Sen. Rand PaulRandal (Rand) Howard PaulTrump formally sends Pompeo nomination to Senate Spending bill delay raises risk of partial government shutdown support Overnight Defense: Senate sides with Trump on military role in Yemen | Dem vets push for new war authorization on Iraq anniversary | General says time isn't 'right' for space corps MORE (Ky.) says the GOP is at risk of turning into “the old white man’s party.”

“I think it’s important that the Republican Party not be seen as a party that’s not welcoming and that [doesn’t] want new people,” the presidential candidate told host Chris Hayes on MSNBC’s “All In."

“I’ve said we need to be a party that has, you know, [people] with earrings, without earrings, with tattoos, without tattoos, black, white, brown, rich [and] poor,” Paul said. "If anything, one of the faults of the Republican Party is we’re not diverse enough.

“When we become the old white man’s party — which we’ve been kind of headed towards for a while — we’re never going to win another election.”

Paul warned Republican voters are making a big mistake by rallying behind Donald TrumpDonald John TrumpKoch-backed group launches six-figure ad buy against Heitkamp Anti-abortion Dem wins primary fight Lipinski holds slim lead in tough Illinois primary fight MORE, who has for months led in national polls of the race.

“We need to be careful about letting the voice of the Republican Party be someone who thinks that all immigrants are rapists or drug dealers,” Paul said of Trump.

“I think that Trump is a disaster for the Republican Party and a disaster for the image that would cultivate and bring new people in, but also for those who have a serious approach for how we would defend the country.”

“That should scare people to death,” he added. "Anybody that’s gotten beyond third grade would say, ‘oh, my goodness, we don’t want a president that is eager to use our nuclear arsenal.'

"We want one, Republican or Democrat, who’s reasonable and restrained and knows it’s a deterrent, but [is] not eager to use it, by any means.”

Paul has been on a media blitz ahead of Fox Business Network's presidential debate on Thursday night.

He has been battling with the network over his exclusion from the main debate stage, arguing he should have made the cut based on his polling numbers. He has asked Fox Business to reconsider letting him on the main stage, and plans to boycott the undercard debate if they refuse.