As Democrats compete for the 2020 nomination in a field that’s shown only flashes of winnowing, Republicans have set their sights squarely on the duo they think could realistically earn the party’s top spot to compete against President Donald Trump: former Vice President Joe Biden and Sen. Elizabeth Warren (D-MA).

Interviews with nearly a dozen senior Republicans, including top officials and strategists on Trump’s re-election campaign and GOP operatives directly familiar with internal deliberations, reveal the president’s party believes the top contenders for the Democratic nomination are unlikely to change. Barring some unforeseen event that would scramble the current field, the long-term strategic moves are centered around a Biden or Warren primary win.

Some of Trump’s election-related moves have been transparent. When Biden’s team launched a $6 million ad buy across Iowa, New Hampshire, Nevada, and South Carolina calling the president “unhinged,” for example, the president’s campaign was right there to counter the effort, unleashing its own ads targeting the former vice president in the same group of states.

Other calculations have been less overt.

Warren’s rise this summer surprised Trump’s inner circle, who counted her out after her widely panned reveal of the results of a DNA test to prove her Native American ancestry following sustained trolling by Trump.

But as Warren’s fundraising and recent polling occasionally surpassed Biden’s, members of Trump’s campaign and political operation began to see her as a more formidable candidate, even as the odds-on favorite to eventually face off against the president.

“It’s impossible not to notice that Elizabeth Warren has moved significantly in the polls,” one Trump campaign official said. “Our job is to be ready.”

Over the past several weeks, Biden’s campaign has responded with heightened urgency to a consistent stream of attacks from Trumpworld, ramping up significantly in late September, when his team launched a full-throttle effort to discredit the former vice president over his son Hunter’s allegedly improper conduct in Ukraine—claims that have been debunked.

In a campaign stop last week in Reno, Nevada, Biden sought to further distance himself from Trump’s taunts, insisting, “I’m not going anywhere,” while addressing the president’s disinformation campaign against his son. Shortly after, Trump spontaneously tweeted that he’d love to face the former vice president in a general election matchup.

“It’s about obliterating [Biden] right now, with the understanding that…Warren is most likely going to soon be the priority when Biden collapses,” a senior Trump campaign aide said.

A Biden campaign spokesman said Trump’s “despicable actions” speak directly to a fear of facing the former vice president in a general election matchup.

“President Trump’s despicable actions—trying to bully foreign governments into assisting his campaign and spreading comprehensively debunked smears—reek of desperation and speak to Trump’s palpable fear of facing Vice President Biden next November,” Biden spokesman Michael Gwin told The Daily Beast.

Trump campaign spokespeople did not respond to requests for comment on this story.

Polling is a key indicator of which Democrats Trump’s associates and allies consider worth spending time on. A Quinnipiac national survey released on Tuesday shows Warren taking the lead over Biden, coming in at 29 percent to his 26 percent. Her rise is a trend that is reflected in the national averages. The latest Real Clear Politics polling average, the two are in a statistical tie, with Warren at 26.6 percent and Biden at 26.4 percent.

“We have to prioritize and every few months we look at who makes sense to dig into,” a GOP strategist said about the two-way nature of the race. “Based on the polling, those two are remaining steady.”

Another Republican aide unaffiliated with the campaign said Warren, who has gained significant traction in the primary since launching her campaign in February, has largely taken the spot that Sen. Bernie Sanders (I-VT) once filled. And some Republicans are planning to repurpose the attacks once reserved for him on Warren.

“Warren basically gives you all the socialist policies in a candidate who’s eight years younger,” the aide said, referencing Warren’s age of 70 to Sanders’ 78.

As his poll numbers have fallen, Sanders has dropped on Republicans’ priority lists, sources familiar with the situation noted. Trump campaign officials say while they had many months ago written off the Vermont Independent as someone who could secure the nomination, they don’t discount his influence in the race.

Beyond Sanders, who has been temporarily off the campaign trail to recover from a recent heart attack, Republicans have also cast aside Sen. Kamala Harris (D-CA) who was, just a few short months ago, considered a major force by Team Trump. During and shortly after the Democratic primary debate in June—when Harris took the fight directly to Biden—many officials in the White House and the Trump campaign identified the California Democrat as a force to be reckoned with, with several Trump advisers messaging high opinions of her performance during the debate in real-time.

However, when Harris’ standing in polls failed to hold, paired with a series of campaign stumbles in early states, virtually every top aide to Trump 2020 and outside Republican operatives went right back to strategizing for a struggle between Team Biden and Team Warren, three knowledgeable sources said.

Now, as a dozen Democrats prepare to compete for the fourth primary debate in Ohio next week, only Biden and Warren are likely to be the focus of Trumpworld’s attention. The event, hosted by CNN and The New York Times in Westerville on Oct. 15, will feature the biggest field yet to appear on stage at one time in the cycle.

“Unless something changes at the next debate, I don’t see that really changing,” the GOP strategist said.