Washington (CNN) Bernie Sanders said Tuesday that he clearly needs a strong voter turnout to win in Iowa on Monday, but he has no expectation of reaching the high-water mark set by then-Sen. Barack Obama in 2008.

"Obama in 2008 ran a campaign which is really going to stay in the history books. It was an unbelievable campaign. In places they ran out of ballots, as I understand," Sanders told reporters after a meeting with the United Steelworkers in Des Moines, Iowa. "The turnout was so extraordinary, nobody expected it. Do I think in this campaign that we are going to match that? I would love to see us do that, I hope we can."

But he added, "Frankly, I don't think we can. What Obama did in 2008 is extraordinary."

Almost twice as many people showed up to caucus in 2008 for the Democratic candidates as had in recent Iowa presidential contests, something largely attributed to Obama's strong appeal and even stronger ground organization. Obama's upset of Clinton in the 2008 caucuses helped launch him to the nomination.

Sanders has been clear that he needs a high turnout at the caucuses Monday with many of his supporters being first-time caucus-goers. But he hasn't placed a cap on his expectations before.

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