Story highlights The Democratic results are a little different than some of the most recent Iowa polls, which mostly found Clinton narrowly ahead of Sanders

The poll results suggest that the key for both Trump and Sanders will be first-time caucus goers

Washington (CNN) Donald Trump is ahead of Texas Sen. Ted Cruz and Vermont Sen. Bernie Sanders has a very narrow edge over Hillary Clinton, an Iowa poll released Monday shows just hours before caucusing begins.

Business executive Trump leads with 31% while Cruz has 24%, giving Trump a larger margin over the Texas senator than he had a week ago. Florida Sen. Marco Rubio has 17% and retired neurosurgeon Ben Carson has 8%.

On the Democratic side, Sanders has 49% while the former Secretary of State has 46% -- a difference of just 3 percentage points, within the poll's 3.2 percentage point margin of error. That result is different from the Des Moines Register poll released Saturday, which also featured a three-point difference, but with Clinton in the lead, 45% to 42%.

That Register poll also featured Trump in the lead, though with a smaller advantage: Trump had 28% to Cruz's 23%, followed by Rubio at 15%.

Monday's poll results suggest that the key for both Trump and Sanders will be first-time caucus goers.

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