Sen. Bernie Sanders said Thursday night that America’s billionaire class is “scared,” and rightly so, after numerous outlets reported that former New York City mayor and billionaire businessman Michael Bloomberg is actively planning to make a late entry into the 2020 Democratic presidential race.

“The billionaire class is scared and they should be scared,” tweeted Sanders, a 2020 Democratic presidential candidate, apparently in response to news that Bloomberg is expected to file paperwork for his possible 2020 Democratic candidacy in Alabama before the state’s Friday deadline.

According to the New York Times, Bloomberg, a former Republican, “has not yet made a final decision on whether to run.”

“But in the first sign that he is seriously moving toward a campaign, Mr. Bloomberg has dispatched staffers to Alabama to gather signatures to qualify for the primary there,” the Times reported. “Mr. Bloomberg and his advisers called a number of prominent Democrats on Thursday to tell them he was seriously considering the race, including former Senator Harry Reid of Nevada.”

The Sanders campaign quickly seized upon Bloomberg’s possible White House bid as evidence that rich Democrats are worried about the prospect of Sanders—who has said he doesn’t think billionaires should exist—becoming the Democratic presidential nominee.

“Three simple points,” Sanders speechwriter David Sirota wrote Thursday night in the campaign’s Bern Notice newsletter. “1. The billionaire class sees the Bernie Surge and is terrified that Bernie is going to win. 2. More billionaires seeking more political power isn’t the change America needs. 3. Bernie is going to win.”

6 weeks ago, @BernieSanders proposed the most far-reaching wealth tax & declared “I don’t think billionaires should exist” https://t.co/4dvNmiymNn Then Bernie began surging in polls https://t.co/eo6JljsrPq And now billionaire @MikeBloomberg is panickinghttps://t.co/NjWdHbSSXB — David Sirota (@davidsirota) November 8, 2019

Sen. Elizabeth Warren (D-Mass.), the other top progressive contender for the 2020 Democratic nomination, responded to reports of Bloomberg’s potential candidacy by tweeting out her campaign’s “Calculator for Billionaires,” which shows the rich how much they would pay under Warren’s proposed wealth tax.

Welcome to the race, @MikeBloomberg! If you’re looking for policy plans that will make a huge difference for working people and which are very popular, start here: https://t.co/6UMSAf90NT — Elizabeth Warren (@ewarren) November 7, 2019

As the Times noted, Bloomberg’s “presence in the race would offer fodder to the party’s rising populist wing, led by Ms. Warren and Mr. Sanders, who contend that the extremely rich already wield far too much influence in politics.”

Some observers suggested Bloomberg is worried about former Vice President Joe Biden’s candidacy and could be entering the fray in a last-ditch attempt to stop the Democratic Party from nominating a progressive.

Progressive activist Jonathan Cohn tweeted Thursday night that “Bloomberg’s decision to enter tells us what we already know: Both Sanders and Warren have real paths to victory, and big donors are afraid that Biden increasingly doesn’t.”