Sen. Bernie Sanders is the early frontrunner for the Democratic nomination and has gotten off to an extremely strong start.

Sanders leads in the polls among declared candidates, and has shattered his competitors in fundraising.

But history also shows that being the early frontrunner is no guarantee of anything.

Sanders' early lead of the 2020 pack is significant because of what it says about the state of the Democratic Party and its metamorphosis since 2016.

By virtually every measure, Sen. Bernie Sanders of Vermont is dominating the race for the Democratic nomination.

He's started off the 2020 race way ahead of a wide field of competitors, defying those who suggested he couldn't build off of the momentum of his 2016 campaign.

However improbable it seemed at the start of his 2016 campaign, the self-declared democratic socialist is a serious contender for the presidency.

With that said, history shows being the early frontrunner does not necessarily guarantee a candidate will go on to win the Democratic nomination.

Here's why Sanders is currently the frontrunner, but also why it might not last.

Sanders is leading in the polls among declared Democratic candidates

National polls for the 2020 Democratic primary consistently show Sanders trailing closely behind former Vice President Joe Biden for the top position. But given Biden hasn't actually announced he's running, this places Sanders in first place among declared candidates.

The latest poll numbers from Morning Consult on who leads the race with Democratic primary voters nationwide show Biden leading overall with 33% and Sanders in second with 25%.

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The next closest contender is Sen. Kamala Harris of California, with just 8% of Democratic primary voters supporting her candidacy.

Among declared candidates, Sanders also has the highest favorability rating (77%), according to Morning Consult, with Sen. Elizabeth Warren of Massachusetts coming in second with a 54% rating. Biden is in first overall with 78%, barely edging out Sanders.

Polling also shows Sanders is the most well-known candidate and winning over young voters as well as Hispanic voters

A recent national poll of 18 to 29-year-old voters from the Institute of Politics at Harvard Kennedy School showed Sanders with a double-digit lead over all 2020 Democrats, including Biden.

The poll showed 31% of young voters support Sanders, with Biden coming in second with 20%.

"Compared to this point in the last presidential cycle, young Democratic voters are more engaged and likely to have an even greater impact in choosing their party’s nominee,' John Della Volpe, director of polling for the Institute of Politics, said in a statement on the poll.

Read more: First-time voters for Bernie Sanders don't care about his age, say he speaks to what matters to them and would've voted for him in 2016

Morning Consult polling provided to The Intercept also found Sanders leading with Hispanic voters overall, with 33% supporting him. All of the other declared 2020 Democratic candidates fall way behind Sanders with Hispanic voters. The only person to come close to his level of support with this Demographic is Biden, with 24%.

The poll also showed Sanders has the highest name-recognition among all declared or potential candidates, coming in at 99%. Biden comes in second with 97%.

A recent Harvard-Harris poll also found Sanders is the most well-known 2020 Democrat — with 88% of responds saying they'd heard of the Vermont senator. Biden also came in second in this poll, with 87% saying they'd heard of the former vice president.

The Vermont senator is knocking campaign fundraising out of the park

Sanders' campaign raised roughly $18.2 million from approximately 525,000 individual donors — with roughly 900,000 contributions overall — in a period of a little over a month after announcing for 2020.

According to Sanders' campaign manager, Faiz Shakir, 20% of donations from the first quarter of 2018 came from new donors and 88% of the money came from people who gave $200 or less. The average donation was $20.

Comparatively, Harris, who comes in second in terms of fundraising so far, raised $12 million in the first three months of 2018.

In the first 24 hours of his campaign, Sanders raised over $6 million, which is more than the $5 million Sen. Cory Booker raised over the course of February and March after announcing his 2020 presidential campaign. Less than a week after announcing, Sanders had raked in $10 million.

Being the early frontrunner has its pros and cons, and doesn't guarantee anything

By many measures, Sanders should be thrilled to be in his current position, especially given how his campaign looked at this point in 2016 compared to now.

After entering the 2016 race as a relatively obscure member of Congress whom many pundits initially dismissed as too radical to be taken seriously, Sanders is now a household name and among the most popular politicians in the country.

Much of the platform he pushed for in the last election has now been adopted by other top Democrats running for the nomination. Over a million people have signed up to volunteer for his campaign. He's drawn in thousands for rallies as he campaigns across the country.

But being the early frontrunner also makes a candidate a target for increased scrutiny, which Sanders is currently experiencing over his tax returns. The senator is under a lot of pressure to release them, and continues to face questions on the subject in interviews. He's pledged to release 10 years of returns after April 15.

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Based on what we know about past elections, being the early frontrunner also doesn't necessarily mean a campaign will go all the way.

In the 2004 Democratic primary, for example, there was also a broad field of candidates. Early on in 2004, polling showed former Army Gen. Wesley Clark as the frontrunner, and put then-Sen. John Kerry in fifth place. Kerry went on to win the Democratic nomination.

In the 2008 election, then-Sen. Hillary Clinton was the early frontrunner. In March 2007, CBS primary polling showed 36% of Democratic primary voters supported Clinton, ahead of then-Sen. Barack Obama (28%), and former Sen. John Edwards (18%). She would remain the frontrunner until January 2008, but lost that status a month later as Obama pulled ahead after winning a number of primary contests.

Simply put, Sanders has gotten off to a strong start but nothing is written in stone.

Much will depend on how Sanders performs in early primary states like Iowa, New Hampshire, and South Carolina. Sanders won a massive victory against Clinton in New Hampshire in 2016, lost narrowly in Iowa, and lost by a landslide in South Carolina.

This election is a different ballgame with a huge number of candidates in which literally anything could happen, and it's a long road until the Iowa caucuses, which are set for February 3, 2020.

Upcoming primary debates in Miami and Detroit will also affect how voters view candidates, and could lead to significant shifts in the polls.

Long story short, it's extremely early in the 2020 campaign season and far too soon to predict who will win the nomination.

What makes Sanders being the early frontrunner significant is what it says about the current state of the Democratic Party, given he's an independent democratic socialist pushing for policies that were seen as far too extreme by mainstream Democrats just a few years ago.