Sen. Bernie Sanders is on a tear.

The independent senator from Vermont burst out of the gates on Feb. 19, as he launched his second straight bid for the Democratic presidential nomination -- and he hasn’t slowed down yet.

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The self-proclaimed ‘democratic socialist’ is drawing huge crowds on the campaign trail and racking up big bucks. He hauled in $18.2 million in fundraising in the first 41 days of his campaign, becoming the overwhelming leader of the pack in the fundraising race among the large roster of White House hopefuls.

The senator consistently registers in second place -- in double digits -- in 2020 polling, trailing only former Vice President Joe Biden. But until Biden officially jumps in, as is widely expected, Sanders for now is the front-runner among declared candidates. This status marks an incredible ascension from the start of the last cycle.

“We have come a long way in the last four years,” Sanders said recently on the campaign trail.

He’s not kidding.

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When the senator first launched his 2016 White House bid, he was considered a far-left fringe candidate who would be a longshot against former Secretary of State Hillary Clinton to capture the Democratic presidential nomination. He was barely taken seriously as he made multiple trips to the early voting states in 2014 and the first half of 2015.

But Sanders caught lightning in a bottle in the summer of 2015, after officially declaring his candidacy. Along with Republican Donald Trump, he tapped into the anger among the electorate with a system that many felt was failing them. And he launched his White House bid at a time when the Democratic Party was moving further to the left.

Whether Sanders sensed this and rode the wave, or whether he is largely responsible for the party's shift since that time, remains to be seen. But the 77-year-old politician is seemingly in the right place at the right time -- at last, after decades in the political wilderness. Today, policies he espouses are virtual litmus tests for the field. Even his presidential primary rivals scrambled to co-sponsor his latest "Medicare for All" bill last week.

Veteran political scientist Dante Scala says that since President George W. Bush’s administration, more and more Democrats “have been willing to identify themselves as liberal.”

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“What we’ve seen over the past decade or so is this decline in moderate and conservative Democrats. A lot more Democrats are willing to say to survey researchers and pollsters that ‘I’m liberal and I’m proud.’ In some way, Sanders was able to capitalize on a trend that was occurring with the Democratic Party,” explained Scala, a political science professor at the University of New Hampshire.

“Sanders capitalized – in 2016 in particular – with a growing sense among both young voters, white working-class voters, that the system was broken and that radical change was necessary to fix it. And I think a lot of that comes out of the great recession,” Scala added. “They wanted a politician who would go big and Bernie was happy to oblige on that.”

Sanders’ crushing defeat of Clinton in 2016 in New Hampshire’s first-in-the-nation primary launched a political juggernaut, sending him into a marathon battle with the eventual nominee that didn’t end until after the primary and caucus calendar.

As he runs a second time, the stridently liberal candidate doesn’t appear to have a problem standing out from the rest of the pack and resonating with younger voters – even with rivals that are four decades younger. And he’s changed the conversation, with many of his fellow White House hopefuls pushing the same proposals that Sanders highlighted on the presidential campaign trail four years earlier.

But Democrats not feeling the ‘Bern’ argue that Sanders was expected to start strong, thanks to his strong name recognition and the extensive nation-wide organization that he built in 2016 and maintained in the ensuing years.

“He starts with a leg up because of running previously but I don’t think it’s an insurmountable advantage by any means,” longtime Democratic strategist Judy Reardon said.

But Scala says Sanders will be successful again because he’s “kind of married liberalism and populism.”

“I think that’s what makes him such a danger to the other 2020 candidates in that he could be what Trump was in 2016. That is, it could be the case that a strong minority bloc of voters who are married to Bernie and they’re not interested in dating,” he said.