Republican Governor Terry Branstad doesn't know who he wants as the Republican nominee, but he can tell Iowans who he doesn't want -- Ted Cruz.

Gov. Terry Branstad of Iowa harshly attacked Senator Ted Cruz of Texas on Tuesday over Mr. Cruz’s opposition to federal ethanol mandates, and he predicted the issue would erode Mr. Cruz’s lead in polls ahead of the state’s caucuses next month.

“I’m convinced he may well lose this because of his stand on ethanol,’’ Mr. Branstad said in an interview.

The governor, a Republican who does not plan to endorse a candidate, predicted a record turnout for both parties in the caucuses in 13 days. A voter surge, he said, would benefit Donald J. Trump and, for Democrats, Senator Bernie Sanders.

Mr. Branstad’s comments amplified remarks he made earlier in the day at the state’s Renewable Fuels Summit in Altoona, which hint at rising concern among Iowa’s corn-growers and the local politicians allied with them that Mr. Cruz may win the caucuses on Feb. 1. If he did, Mr. Cruz would be the first candidate to do so while pledging to phase out the federal ethanol standard, which requires corn-derived ethanol and other biofuels to be mixed with gasoline.

Asked at the summit if he wanted Mr. Cruz to lose the Republican caucus race, Mr. Branstad said, simply, “Yes.’’

Ethanol is a huge part of Iowa's economy, so it's understandable that Branstad might oppose Cruz, who opposes alternative fuels as a matter of principle.

At the same summit, Donald Trump went all apocalyptic.

Trump says we're in times medieval times because Christians heads are being chopped off overseas. This is a speech about ethanol...

— Lucia Graves (@lucia_graves) January 19, 2016

So maybe it wasn't really all about ethanol at the summit, which tells me there's more to Branstad's Cruz repudiation than alternative energy sources.