Thousands of people packed Safeco Field Friday evening to hear Bernie Sanders speak at the Democratic presidential candidate's second large rally Seattle in less than a week.

Campaign organizers estimated a little over 15,000 people rallied around Sanders as he tried to energize voters before Washington's Democratic caucuses.

Saturday's nominating contest is expected to draw tens of thousands of Washington voters who will ultimately determine how 101 of the state's Democratic delegates will be awarded.

"We are doing well in this campaign because we're telling the American people the truth. The truth is we have a campaign finance system that is corrupt," Sanders told his cheering supporters at Safeco.

Sanders went on to preach his mantra about income equality, touting an economy that benefits the middle class, not the wealthy. The Vermont senator also talked about reforming the U.S. criminal justice system, equal pay for equal work, and for the young people in the crowd, Sanders pushed his platform to eliminate student loans.

"We should be rewarding people for getting an education, not punishing them," Sanders said.

The rally ended with big cheers at the end, when Sanders vowed to make history by winning the Washington state caucuses Saturday.

Hillary Clinton has a comfortable lead over Sanders in the delegate count. Based on primaries and caucuses to date, the former secretary of state leads Sanders 1,223 to 920.

Stumping in Oregon Friday afternoon ahead of his visit to Seattle, Sanders got a rousing welcome in progressive Portland, where more than 10,000 people attended his rally at Moda Center, home of the Portland Trail Blazers.

The Democrat said at the rally it would be a disaster if Donald Trump were elected president, but Sanders said Americans are too smart to let that happen.

Watch: One-on-one interview with Bernie Sanders