Sen. Bernie Sanders acknowledged Monday that he has been hurt by Oregon’s restrictive rules on primary voters, but he said he remained confident of victory if Democrat turnout is high.

“We do much better when independents are allowed to vote,” Sanders said in a telephone interview. He noted that many of his supporters were “non-traditional voters” who often register as non-affiliated.

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In Oregon, only voters registered as Democrats at least 21 days in advance of Tuesday’s election deadline can participate in the party’s primary. That may be one factor driving last week’s surprising poll showing Hillary Clinton leading Sanders in Oregon.

Sanders didn’t challenge the poll results but said he thinks he will win if turnout is high. As of Monday morning, 37 percent of Democrats had returned their mail ballot, according to the Oregon Elections Division.

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Turnout would have to double by 8 p.m. Tuesday to equal the 75 percent who voted in the 2008 Democratic presidential primary between Clinton and Barack Obama. That year, just under 40 percent of voters turned in their ballot in the last two days.

Sanders has called several Oregon media outlets in recent days hoping to spur his supporters to vote. He has held two campaign rallies in Oregon in the last two months.

“If we do well in Oregon tomorrow, if we do well in Kentucky” and the six remaining states in the primary season, Sanders said, "we have a path to a victory.”

Clinton has not visited during this election cycle, though former President Bill Clinton campaigned in Bend and Portland on her behalf.

In the Monday interview, Sanders said that regardless of the outcome of the Democratic contest, he would do “everything I can to make sure” that Donald Trump does not become president.

“This is a man who does not clearly have the temperament to become the president of the United States,” he said.