Nobel winner Robert Shiller said he doesn't think home prices will fall if the limit on the amount of mortgage debt one can deduct is cut in half by President Donald Trump’s tax reform.

However, the Yale University economics professor recently told CNBC that he does think a cut to the property tax deduction could be "a substantial hit to people who are paying a lot of property taxes."

People often act irrationally when it comes to housing, he explained, and historically home prices haven't reacted "at all predictably to changes in things like interest rates."

"The general idea is it would push prices down if people are rational," which Shiller says they are not when it comes to housing.

To be sure, the GOP's proposed tax overhaul includes limits on the deductions for mortgage interest, state taxes and property taxes.

However, when asked what he thought the impact would be to the overall real-estate market, he was blunt. "It's not big," said Shiller, who also helped develop the widely-followed S&P/Case-Shiller Home Price Indices.

"That is going to be a substantial hit to people who are paying a lot of property taxes, and it might be a consideration that you make before you buy a big mansion in some high property tax state," said Shiller, who was awarded the Nobel Prize in Economic Sciences with Eugene Fama and Lars Peter Hansen in 2013.

"I tend to think it's not as great as you imagine because people are people, and I don't find that historically home prices have relied at all predictably to changes in things like interest rates," said Shiller.

However, thousands of homeowners in Republican-leaning areas who could be hit by that elimination or reduction of tax breaks for homeowners, a Reuters analysis of federal mortgage and tax data shows, potentially opening those districts to a Democratic challenge in the November 2018 mid-term elections.

The plans are expected to affect mainly the Democratic-leaning “blue states” such as California, New Jersey and New York where homes are expensive, mortgages are huge and state and local taxes tend to be high.

But while these blue states will be hardest hit, county level data also shows there is a significant number of Republican enclaves in districts expected to be hotly contested in next year's polls that will feel the pain. Republican leaning pockets in blue or swing states, such as Orange County, California, or Loudoun County, Virginia, tend to have high property values – and thus the higher mortgages.

Many of these areas also tend to have higher state and local income taxes.

Larry Sabato, director of the non-partisan Center for Politics at the University of Virginia, estimates that there are 16 counties where 2018 races will be toss-ups between Republican incumbents and Democratic challengers.

Reuters data shows that almost half of those counties have an above-average share of new mortgages worth more than $500,000, which is a proposed cap for tax deductions. The results are similar for districts selected as 50-50 ones by The Cook Political Report, a non-partisan newsletter that analyzes U.S. elections.