Those who signed the letter, including five Democratic presidential candidates, did not mention Trump’s comments at a fundraising dinner on Tuesday.

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But in a call with reporters, Grassley called the president’s comments “idiotic,” according to the Des Moines Register.

“Hillary wanted to put up wind. Wind!” Trump said, referring to the energy policies of his 2016 Democratic presidential opponent, Hillary Clinton. “If you have a windmill anywhere near your house, congratulations, your house just went down 75 percent in value. And they say the noise causes cancer. You tell me that one, okay?”

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A White House spokesman did not immediately respond to a request Wednesday by The Washington Post for evidence to back up the president’s claim.

A 2014 study found there are some risks to sustained exposure to noise from wind turbines, including sleep disturbance. But the peer-reviewed research published by PLOS ONE dismissed possible links to several other conditions, including headaches and vertigo, and did not mention cancer.

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According to the Des Moines Register, Gov. Kim Reynolds (R) also answered questions about Trump’s comments but would not weigh in on the president’s claim that turbine noise causes cancer.

“You know how those things change,” she said. “One year, coffee’s good for you. The next year, coffee causes cancer.”

Wind energy has become a major industry in Iowa, the nation’s first presidential nominating state, which perhaps explains why so many presidential hopefuls signed the senators’ letter. Those included Kirsten Gillibrand (N.Y.), Kamala D. Harris (Calif.), Amy Klobuchar (Minn.), Bernie Sanders (I-Vt.) and Elizabeth Warren (Mass.).

Other signers were Sens. Michael F. Bennet (D-Colo.), Sherrod Brown (D-Ohio), Thomas R. Carper (D-Del.), Cory Gardner (R-Colo.), Martin Heinrich (D-N.M.), Angus King (I-Maine), Edward J. Markey (D-Mass.), Jack Reed (D-R.I.), Michael Rounds (R-S.D.), Tina Smith (D-Minn.), Sheldon Whitehouse (D-R.I.) and Ron Wyden (D-Ore.).