Sanders won by massive margins in Alaska and Washington, which he said will propel his momentum going into the April contests.
"We knew things were going to improve as we headed west," Sanders told supporters Saturday evening at a rally in Madison, Wisconsin, a crucial state that holds its primary April 5. "We are making significant inroads in Secretary Clinton's lead and we have, with your support coming here in Wisconsin, we have a path toward victory."
As expected, Sanders won Alaska and Washington state. But the real news is in the sheer size of his victory.
In Alaska, he was winning by nearly 60 percentage points with 73% of the delegates in at 6:40 p.m. ET. In Washington state, he was ahead by more than 50 points with 31% of the delegates in. If that margin holds, he'll outpace then-Sen. Barack Obama's performance in Washington in 2008.
These caucus states -- largely white and rural -- are the type of places Sanders traditionally does well. In order to win the nomination, he must replicate this success in other, more ethnically diverse states that hold primaries, as he did in Michigan last month.
In theory, it's possible. But the reality is tough.
The next showdown between Clinton and Sanders will be in Wisconsin, a state that will serve as a key test for both campaigns.
But from there, the campaign calendar heads eastward into prime Clinton territory. Late April contests in New York, Pennsylvania and Maryland -- where a total of 619 delegates are at stake -- strongly favor the former secretary of state.
"He has momentum and he has money, but he doesn't have the math," said CNN's John King.
That said, the sheer size of Sanders support in these contests underscores his success in energizing a segment of progressive-minded voters who are making a statement about the direction they want to take the Democratic Party. And the magnitude of his wins on Saturday will let him spend the next few weeks making the case that he's closing the gap in the battle for delegates -- even if Clinton is more likely to get across the finish line.
Sanders needs to pull an Obama
To win the nomination, Sanders needs the help of the superdelegates. And right now, most are with Clinton.
But that could change, and history proves it. Early in 2008, when Clinton was running against then-Sen. Barack Obama, she had the super delegates on her side. But when Obama started gaining momentum across the country, he slowly peeled away their support until he won the nomination.
Eight years later, Sanders would have to do the same if he wants to clinch the nomination. Sanders needs to take the momentum he gained Saturday in the western states and repeat it in the upcoming contest in Wisconsin on April 5 and beyond.
"If he does that, some of the superdelegates will get the jitters and either go back to neutral or maybe switch," King said.
Sanders is clearly looking to build off the Saturday victories as a key opportunity to do just that.
"It is hard for anybody to deny that our campaign has the momentum," Sanders said in Wisconsin after the results were announced. "That is what momentum is about."
Repeating Obama's success, however, will be tough for Sanders. The western states that held contests Saturday played to his strengths, but he has not yet replicated the upset he won in Michigan in other big, diverse states. Sanders must prove that he can do that if he wants to repeat Obama's come-from-behind win.
Clinton focused on the general election
Clinton isn't showing any sign that she's worried about Sanders' success. She's more focused on another rival at this point: Donald Trump.
Look no further than a speech she delivered Wednesday in California responding to the terror attacks in Belgium, where she focused on laying the groundwork for the general election rather than her primary with Sanders.
"If Mr. Trump gets his way, it will be like Christmas in the Kremlin," Clinton said, referring to her opinion of the impact the GOP front-runner would have on the role of the United States in the world. "It will make America less safe and the world more dangerous."
Her remarks made no attempt to refute Sanders' view of foreign policy or how he we would respond to a terrorist attack. As CNN contributor S.E. Cupp put it, "Sanders can have Washington, Alaska and Hawaii today -- she is already on to November."
Still, Clinton's team is using the Sanders victories on Saturday to fire up fundraising efforts.
"We're still being outspent on the air in key states, we haven't caught up in online fundraising, and our opponent could do very well in today's caucuses in Washington, Alaska, and Hawaii," Clinton campaign manager Robby Mook said in a Saturday email to supporters that went out shortly after Sanders was projected to win Alaska.
Republicans get a break
There's no rest for the weary, the old saying goes.
But on Saturday, political junkies got something of a catnap from the dramatic saga of the Republican presidential nomination. Saturday's caucuses were solely for Democratic voters, which gave the remaining Republican candidates and campaigns a chance to re-focus on crucial future contests.
Still, the weekend wasn't drama-free.
On Friday, Texas Sen. Ted Cruz found himself publicly denying salacious allegations in the pages of The National Enquirer. Cruz blamed Donald Trump's "henchmen"— Trump ally Roger Stone was quoted in the Enquirer story -- for distributing "complete and utter lies." (CNN has no reporting suggesting the tabloid report is accurate.)
On Saturday, Trump attempted to keep the story alive on social media. And Cruz hammered Trump.
Meanwhile, Trump took a brief break from the campaign trail to spend time in Florida. The race will pick back up in full steam next week as the three remaining contenders—Trump, Cruz and Ohio Gov. John Kasich— look toward Wisconsin, with 42 delegates at stake.
For his part, Sanders made sure to slam the GOP during his rally in Madison.
Republicans are "not just an embarrassment for the American people," he said. "They are an embarrassment for sane Republicans."
Sanders' feathered friend
A small bird landed on Sanders' lectern in the middle of a campaign rally in Portland, Oregon, Friday, sending his supporters into a state of rapturous ecstasy. Video of the moment between Bernie and the bird went viral online, as Sanders fans shared it on social media.
What does it mean? Nothing, really, but it did provide a moment of levity and joy for a candidate known more for his dour demeanor than a sunny disposition.
Sanders' campaign moved quickly to capitalize on the unlikely moment, tweeting — (Get it? Tweeting. Because it is a bird) -- a graphic with Sanders and the bird while voters were caucusing.