If Donald Trump wins the presidential nomination, it will be terrible for the Republican Party, says Ron Paul, the former GOP presidential hopeful whose son is running for the White House.

"It would be very bad if he was to get the nomination," Paul said in a Thursday interview with CNBC's "Futures Now." "The party would be severed in two pieces."

Further, said the libertarian former congressman from Texas said, "he wouldn't win, and it would be devastating to the markets, because then you'd have Hillary [Clinton]," whose tax policies would hurt the economy.

Read MoreHedge fund billionaire supports this GOP candidate

Trump leads the GOP field, enjoying the support of 35 percent of Republican primary voters, according to a new CBS News/New York Times poll. That's a substantial rise from 22 percent in October. The new poll, conducted from Friday to Tuesday, found that support for Paul's son, Sen. Rand Paul of Kentucky, is flat at 4 percent.

On the Democratic side, Clinton's support is rock-solid at 52 percent.

The elder Paul said the Republicans could actually force the nomination away from Trump — but at a hefty cost.

"In a way, Republicans can decide who their candidate is. They can write the rules any way they want. But if they deny [the nomination] to Trump, Trump would run as an independent."

Read More Trump's comments cost him cash



If "they can't push him out, then somebody else would enter," Paul said. In that way, either a Trump win or a situation in which the nomination is forced away from Trump could result in a split Republican ticket.

"But I think it's more likely that Trump would run as an independent than the mainstream having an independent candidate," Paul said. Trump had said he would consider such an option but later promised not to do so.