Pollster Scott Rasmussen said he's going to be keeping a close watch on more than two dozen counties in Iowa, as the results of the Iowa Democratic caucuses are reported on Tuesday night. That's because these counties may reveal a lot about President Donald Trump's hopes to win re-election in 2020.

Rasmussen is tracking so-called "pivot counties," which are counties that went for President Barack Obama in 2008 and 2012, but then flipped and voted for President Trump in 2016.

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"There are 206 pivot counties in the country," explained Rasmussen on Fox Nation's "Deep Dive."

"They voted twice for Obama and then for Trump," he continued. "Thirty-one of them are in Iowa and they're all in the eastern part of the state. These are people who were looking for change when they voted for Barack Obama. They didn't like the change at the end of the day."

"They went strongly for Obama, and after eight years they said, 'We want Donald Trump,'" he reiterated.

These are also regions that the Democrats want to swing back into their column, as they get set to take on President Trump in the general election in the fall.

These "pivot counties" are significant, according to Rasmussen, because while they represent only a small percentage of the national electorate, they have a disproportionate impact on the final tally.

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"All across the country, these voters accounted for only 5 percent of the votes that were cast, but they accounted for 51 percent of the net popular vote gains that Donald Trump enjoyed," said Rasmussen.

"I'm going to be watching to see where the Democratic enthusiasm is. If these pivot counties in eastern Iowa show low turnout in this caucus, you're going to say, 'OK, they've made their decision for 2020,'" said Rasmussen, arguing low turnout would indicate that these voters are not swinging back to the Democrats.

However, Rasmussen concluded, "If they surprise us, if there's a huge turnout in those counties, then we're going to have to reevaluate."

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