It appears that top Democratic contender in the 2020 presidential elections, Senator Bernie Sanders, is making the party's mainstream nervous, and it's not because they are afraid he can't win against President Donald Trump, it's because they think he can.

The self-proclaimed Democrat socialist's performance, ever since his announcement to run for 2020, has been strong. Sanders is just behind former Vice President Joe Biden in the poll rankings, however, Biden is yet to announce his candidacy for the run. 

The Vermont senator took the lead in an Emerson poll on Tuesday and has raised over $18 million so far in the first quarter of 2019, marking the highest amount of money raised out of nearly 19 Democrats running for the White House. Sanders, overall,  is right behind Trump, who has raised over $40 million for his 2020 campaign.

The founder of progressive news network TYT, Cenk Uygur, told CNBC that Sanders, at the moment, had a better chance of winning the polls than the rest of the Democratic field combined and that his followers who made him a phenomenon in the 2016 polls are here to stay.

Uygur, who supported Sanders in the 2016 elections, has not yet decided who he will back yet, but his favorites so far are Sanders and Massachusetts Senator Elizabeth Warren. Uygur, while referring to the establishment's concern raised in a New York Times article, said that Sanders is only going to get stronger. The article cited party insiders who fear that the Vermont Senator's campaign could complicate the party's efforts to stop Trump from winning the 2020 election.

"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," David Brock, a political consultant, told the Times, adding that according to his discussions with other operatives, an anti-Sanders campaign will commence soon.

"The big Dem donors are not worried he’s going to lose the general election, they’re worried he’s going to win,” Uygur tweeted on Tuesday, pointing that big-money donors who are backing the party's mainstream candidates will lose their positions of power if Sanders wins.

“The people with the most money will lose all power, they will not be rewarded,” he said. “All their power is in giving money to politicians and controlling them. Bernie Sanders doesn’t want their money. They are going to fight Bernie Sanders harder than any Republican will.”

Attacking Sanders will “force everyone to rally around him,” Uygur said. “That’s why Bernie has always stood an excellent chance of winning. They can’t take away a small donor base. The more they attack him, the more he will raise.”