Some of the most striking evidence yet that Trump is impacting Republican voters’ vote-by-mail attitudes rests in a Rice University survey, obtained by the Washington Examiner, of 1,002 registered voters in Harris County, Texas — the most populous county in the state that has a larger portion.

The survey found that 68% of Democrats said they would be very likely to want to vote by mail, but only 42% of Republicans said the same. About 38% of Republicans said they would be very unlikely to vote with a mail-in ballot, compared to 14% of Democrats.

Bob Stein, a political science professor at Rice who conducted the survey, said that he noticed a difference between Republicans who answered earlier in the survey, which started on March 27, and the final result, which included all the answers through May 4.

Before Trump started vigorously attacking vote-by-mail, particularly in a notable White House briefing room press conference, about 46% or 47% of Republicans said that they would be very likely to vote by mail.

“So, it dropped 4, 5 points,” Stein told the Washington Examiner. “It was very clear to us that the polarization was great, but it got worse.”