Even with big crowds and "Bernie-mentum," Democratic presidential candidate Bernie Sanders says he will not run as a third party candidate in 2016 if he loses the nomination.

"For a lot of reasons the only way at this particular moment in history where we can run an effective campaign is within the Democratic Party," Sanders said at a Q&A session with the United States Hispanic Chamber of Commerce in Washington, D.C., on Thursday. "If it happens that I do not win that process would I run outside the system? No, I made the promise that I would not. And the reason for that is that I do not want to be responsible for electing some right-wing Republican to be president of the United States."

Many liberals blamed Ralph Nader's Green Party candidacy for throwing the 2000 presidential election to George W. Bush.

Sanders, the longest-serving independent in Congress' history, has a history of running as a third party candidate, though he caucuses with the Democrats in the Senate. He even thought of running as an independent this time, but decided to represent millions of Democrats who think their national party is too conservative.

The most recent national polls have Clinton at 55 percent and Sanders trailing at 17 percent. Sanders says that he doesn't want to weaken the Democratic Party by running as an independent, even though some of his supporters would prefer he did so.

"I was contemplating what to do, there were a lot of people who said, 'Bernie why don't you run as an independent?' " Sanders said. "The Republican Party is an extreme right-wing party. The Democratic Party is too conservative, too cozied up with big money and corporate America. They said you gotta run outside of the two-party system."

But Sanders instead decided to stake his progressive campaign on the Democratic primaries.