For a man obsessed with crowd size, President Trump has been eerily silent about a rally that’s the largest yet by a rival running to take him on in the 2020 election.

On the same day that Sen. Bernie Sanders (I-VT) got over 25,000 people to show up in support of his campaign at an event in Queens on Saturday, Trump was preoccupied with two entirely different ex-presidential contenders from 2016 and a current one polling in the low single digits.

“So now Crooked Hillary is at it again! She is calling Congresswoman Tulsi Gabbard ‘a Russian favorite,’ and Jill Stein ‘a Russian asset.’ As you may have heard, I was called a big Russia lover also (actually, I do like Russian people. I like all people!). Hillary’s gone Crazy!” the president tweeted.

Trump was referring to a back-and-forth that erupted between Clinton allies and Gabbard over apparent allegations that the former Democratic presidential nominee views the Hawaii congresswoman as a favorite of the Russian government. In addition, Stein, who previously launched a third-party bid, has been criticized by some Clinton loyalists as having helped sway the election in the president’s favor.

But as Trump fixated on Clinton and stayed silent on Sanders over the weekend, some Republicans were eyeing the force behind his rally—where he was introduced by his most coveted endorser yet, Rep. Alexandria Ocasio-Cortez (D-NY)—with fresh attention.

“Anyone who counted out Bernie Sanders is going to be wrong,” former 2016 Trump campaign adviser Michael Caputo told The Daily Beast. “I see Bernie as far more formidable now than he ever was. With the endorsements from the freshman congresswomen, I think it brings a new life back into his campaign,” Caputo said, referencing both Ocasio-Cortez and Rep. Ilhan Omar (D-MN), who also endorsed Sanders.

Caputo, a veteran Republican and pro-Trump campaign operative, sees many similarities between the Trump voters of 2016 and potential Trump or Sanders voters of 2020. With much of the presidential primary buzz centered around former Vice President Joe Biden and Sen. Elizabeth Warren (D-MA), he said it’s Sanders’ message that most closely aligns with swing voters—particularly in the Rust Belt—who went for Trump.

“We see the support for socialism and for progressive values going up every year. Bernie Sanders brought that brand of politics to the presidential level,” he said. “You’d have to be pretty overconfident not to see the challenge he creates not just for Donald Trump but for the Democratic Party.”

The Queens rally was a must-show of force for Team Sanders. In the days leading up to the event, and following the fourth Democratic debate in Ohio, the campaign sent out emails and social media blasts in hopes of generating the kind of momentum that would be enhanced by Ocasio-Cortez’s presence. In a fundraising email they called her one of “the great political phenomenons in modern American history.”

“ I see Bernie as far more formidable now than he ever was. With the endorsements from the freshman congresswomen, I think it brings a new life back into his campaign. ” — former 2016 Trump campaign adviser Michael Caputo

Some Democratic operatives unaffiliated with any campaign publicly acknowledged the endorsement. Brian Fallon, who served as Clinton’s national press secretary in 2016, wrote on Twitter “few endorsements actually matter in campaigns. But this one does.”

Sure enough, the optics boost followed on Saturday, where Sanders beat the approximately 20,000 people that showed up at Warren’s September rally in Manhattan’s Washington Square Park, as well as Sen. Kamala Harris’ (D-CA) campaign kickoff in Oakland, California, in January.

“When I look at this huge crowd, brothers and sisters, I have no doubt that the political revolution is going to sweep this country, sweep Donald Trump out of office and bring the change that this country has long needed,” Sanders said.

When asked about what Saturday’s showing could mean for the campaign, veteran Republican strategist Doug Heye told The Daily Beast “you can’t argue with the crowd size.”

“But crowd sizes alone don’t win primaries and caucuses,” he continued.

Heye acknowledged a strong physical emergence for Sanders, but also pointed indirectly to Warren as a formidable opponent in the Democratic primary.

“The Sanders campaign still needs to demonstrate what states they can win, especially when that means beating a candidate positioning herself as sort of a ‘Bernie-lite,’” he said, without referencing the Massachusetts senator by name.

In the 2016 primary, Sanders won Michigan and Wisconsin against Clinton, two critical battlegrounds that ultimately went for Trump in the general election, and which a senior Trump campaign official acknowledged to reporters are top targets again.

While Sanders didn’t specify which states he’ll visit next, the Vermont senator said he plans to crisscross the country with Ocasio-Cortez to campaign on behalf of working people.

During his Saturday rally, the 78-year-old Sanders tested out a new applause line, saying he is “more than ready” to take on several political hurdles to come, after questions about his age following a recent heart attack swirled around his campaign.

“I am more than ready to take on the greed and corruption of the corporate elite and their apologists. I am more ready than ever to create a government based on the principles of justice,” Sanders said at the outdoor event. “To put it bluntly,” he went on, “I am back.”

While Trump has been more focused recently on Biden, primarily targeting him over debunked allegations that his son Hunter was engaged in misconduct in Ukraine and China, Republican strategists and those in the president’s inner circle have recently expressed some increased anxiety over a rising Warren, The Daily Beast has reported, and some view the Democratic primary as increasingly becoming a two candidate race between Warren and Biden.

But for other Republicans, including in the Republican National Committee, Sanders is just as deserving of their attention and rapid attacks. And if the president himself is hesitant at times to jab Sanders on Twitter—in contrast to a flurry of tweets he’s fired off about Warren and Biden in recent months—allies from the Republican Party establishment to conservative media stars are quick to pick up the slack.

“Bernie Sanders and Alexandria Ocasio-Cortez’s touting their job-killing, tax-increasing socialist agenda to rally New York liberals is about as unsurprising as it gets,” RNC Spokesman Steve Guest told The Daily Beast when asked about Sanders’ strength. “Good luck to Democrats trying to sell these far left, fringe ideas to Americans anywhere outside of the coasts.”

“Socialism Sucks,” right-wing internet provocateur Charlie Kirk tweeted the day after Sanders’ rally. “Cuba is now breeding ostriches to feed its starving masses They eat ‘steaks’ made of dried grapefruit rind The Cuban Ag commissioner is encouraging people to eat rodents he says taste ‘better than beef’ This is what Bernie’s America will look like.”