Bernie Sanders is emerging as the front-runner to win the 2020 Democratic presidential nomination.

Sanders, the Independent senator from Vermont, has surged to an early lead in fundraising.

His poll numbers are better than any other candidate in the race - and are rivaled only by former Vice President Joe Biden, who has yet to enter the contest and who has been beset by concerns over his behavior toward women.

Even Sanders's gambles are paying off for now. A town hall-style event broadcast by Fox News on Monday garnered an audience of more than 2.5 million. The Vermont senator's assured performance drowned out criticism from some Democrats who were dubious about the left-wing senator appearing on the network.

Overall, the message is clear. Sanders is the one to beat.

"Right now, he is the front-runner," said Karine Jean-Pierre, the chief public affairs officer for MoveOn, a progressive group. "He is leading in the fundraising. He is leading in the polling - except for Biden, who has not jumped in yet. ... Bernie's start has been impressive. Clearly his base is still with him and still excited."

The fervency of Sanders's base will be especially important given the size of the Democratic field.

He came up short against Hillary Clinton in 2016, but that was, in essence, a two-person race. This time around, there are about a half-dozen serious contenders for the nomination and plenty of other candidates who will claim smaller slices of the pie. Those dynamics make the apparently unshakeable loyalty of Sanders's backers very potent.

Months ago, some in the media speculated that Sanders would have a tough time in this cycle because of competition from other left-leaning candidates - notably Sen. Elizabeth Warren (D-Mass.). Other contenders such as Sen. Kamala Harris (D-Calif.) have sought to appeal to more centrist voters even while backing trademark Sanders proposals such as "Medicare for All."

But so far, there is little sign that those candidates have eroded Sanders's popularity.

"He was there first, and he has been there for a long time," said Tad Devine, a Democratic strategist who has worked for Sanders in the past - including the 2016 campaign - but is not doing so this cycle.

Citing issues such as tuition-free college and an increased minimum wage as well as Medicare for All, Devine added, "I think the fact that others have come over to his side has only put those issues much more into the mainstream."

Still, the skeptics remain.

The Sanders doubters question whether a self-described democratic socialist who would be 79 on Inauguration Day 2021 is really the best candidate to defeat President Trump next November.

Some people who hold this view acknowledge that Trump is relatively weak - but they argue this makes it vital that Democrats choose a standard-bearer who does not give the president extra ammunition.

"A typical president with an economy this strong would probably be in the 50s or 60s" in terms of their approval rating, said one Democratic strategist who requested anonymity to speak candidly.

"Trump has difficulty breaking 45. But the fundamental problem with Sanders's candidacy is that it is based on the assumption that the country is ready to go in a fundamentally more radical direction. That is a significant jump in logic," the strategist added.

Others are even clearer in their distaste for the idea of a Sanders nomination. David Brock, a Democratic activist and Clinton loyalist, told The New York Times in a story published Tuesday that an anti-Sanders campaign among Democrats should begin "sooner rather than later."

The imperative for such a move, Brock told the Times, is that "there's a growing realization that Sanders could end up winning this thing, or certainly that he stays in so long that he damages the actual winner."

The idea of a Democratic establishment effort to hobble Sanders is fraught with difficulty, however - not least because of the enmity dating back to 2016, when Sanders backers were adamant that the party apparatus, including the Democratic National Committee, sought to aid Clinton at their candidate's expense.

Even the Democratic strategist who requested anonymity was dubious about any such move.

"You are not going to be able to stop Bernie Sanders if he has the support. It's as simple as that," this source said. "The idea of stopping him is eerily similar to the language Republicans used about Donald Trump. Either you get a more viable alternative or you don't. You are not going to beat Bernie Sanders with establishment shenanigans."

Devine, the former Sanders aide, argued that any such effort was almost sure to backfire.

"It seems like some people ... feel they need to stop his momentum. But if they do that, they are going to help his momentum. He is going to feed off it and they are going to exploit that in terms of fundraising tremendously," he said.

The president has continued to attack Sanders, suggesting that he is far outside the American mainstream. "So weird to watch Crazy Bernie on @FoxNews," Trump tweeted on Tuesday, referring to Sanders's town hall the previous night.

But whether a Democratic Party whose base seems enamored of Sanders and other progressive figures such as Rep. Alexandria Ocasio-Cortez (D-N.Y) is willing to back away from the Vermont Independent is very much in doubt.

Even Sanders skeptics insist that his rivals for the nomination need to rid themselves of complacency - and fast.

"These other campaigns better wake up and realize that Bernie Sanders is a formidable candidate," said the Democratic strategist. "He is not going to lose by some whim of the gods. He is going to lose if you beat him. And right now, there is no one beating him."

The Memo is a reported column by Niall Stanage, primarily focused on Donald Trump's presidency.