Merkley was a guest on CNN's "New Day," and responded to a tweet by likely GOP nominee Donald Trump
urging Sanders to run as an independent because "the system is rigged against him."
Sanders would "absolutely not" run as an independent, Merkley told host Chris Cuomo, noting that the Vermont senator is mindful of the way the 2000 election played out.
"You know, Bernie went into this and he said, 'There's no way I'll be Ralph Nader.' We're not going to split the party, we're not going to empower the Republicans. He understands the damage that Bush did to this nation, and is not going to allow Trump to follow on and do even more damage," Merkley said.
Trump has pressed Sanders to run as an independent before, tweeting similar advice to him in in April only to be dismissed by Jane Sanders,
Merkley also previewed the Democratic primary in Oregon tomorrow, saying he's seen strong support at town halls around the state for Sanders. But Merkley acknowledged that the state's closed primary -- which prevents Sanders-friendly independents from voting -- is "unfortunate" for his candidate.
"It is true that in Oregon a lot of the independents who have been coming out to the Bernie rallies aren't able to vote. That's unfortunate," Merkley said.
"But I can tell you, I do a lot of town halls and when people come to my town halls I see Bernie shirts, I see Bernie buttons. I haven't seen a Hillary button yet, and that tells you a couple things," he added.
"One, how Bernie's message is resonating on these core issues facing America. And, second, if Hillary does end up being the nominee -- as you say, the math is difficult, the path is uphill -- she's going to need to reach out and understand these core issues that are so connecting with ordinary individuals."