Fox News contributor and former George W. Bush speechwriter Marc Thiessen theorized Tuesday that the Senate impeachment trial had a negative impact on the turnout for Monday night's Iowa Democratic caucuses.

"It was a very low turnout," Thiessen said on "The Story with Martha MacCallum." "There is an enthusiasm gap right now. And it's partly because of impeachment."

IOWA CAUCUS MESS LEAVES EVERY LEADING 2020 DEM CLAIMING MOMENTUM INTO NEW HAMPSHIRE

According to the Iowa Democratic Party, Monday night's turnout roughly matched that for the 2016 Democratic caucuses, which was significantly lower than the historic high of 2008.

"The Republican base is hugely energized to go out and vote for Donald Trump," Thiessen said. "And because they're about to lose the impeachment fight, that they [Democrats] spent three years trying to get to this moment and they're now losing, their enthusiasm is dissipated."

The former speechwriter did add that there was some good news for Democrats because the partial results released Tuesday were a good sign for moderate candidates.

"The good news for Democrats is, is that it was a really good night for the moderate lane in Iowa because ... Joe Biden was found to be unviable, in the words of the Iowa caucuses," said Thiessen, who added that Biden's decline presented an opportunity for Sen. Amy Klobuchar, D-Minn., or former New York City Mayor Michael Bloomberg.

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Former Democratic National Committee interim chairwoman Donna Brazile dismissed the notion that Biden was down and out.

"I think many of us knew going into yesterday that Biden really is not the candidate for Iowans. He's not their demographic. So I wasn't surprised that he came in fourth place or even fifth place," Brazile said. "Once we get the rest of the numbers, the proof in the pudding is, as you well know, Nevada [and] South Carolina. That's more Biden territory than Iowa [and] New Hampshire."