For much of the past year, Donald Trump and his allies have speculated that Joe Biden would not end up as the Democratic presidential nominee 鈥 suggesting without evidence that he would step down before the convention and be replaced by another candidate.

Now, with Biden facing an increasingly uncertain political future amid the fallout from his shaky debate performance, Republicans are trying to determine what the Democratic incumbent stepping aside would actually mean for the Trump campaign. And some believe the path back to the White House would likely be easier with Biden at the top of the ticket.

Trump and his allies have relished the extended spotlight on Biden this week, with the former president making the rare decision to lay low at his New Jersey club and allow Biden to be the story. Trump has no public events on his schedule, and his campaign surprised some aides and advisers by telling them to enjoy the Fourth of July holiday.

鈥淐haos is our friend,鈥 a person close to Trump said.

Meanwhile, campaign advisers and key allies have been calling reporters and friendly Democrats, hunting for any clues into what might happen next should Biden ultimately walk away from his reelection bid.

Until now, the campaign and its allies have largely ignored Vice President Kamala Harris in waging their attacks against the Biden administration. But there are signs that posture is changing. On Wednesday, a super PAC aligned with Trump, MAGA, Inc., launched its opening salvo against Harris by attacking her oversight of Biden鈥檚 border policies in an email. It asked if Harris is 鈥淭he Best They Got?鈥

Trump鈥檚 campaign insists that nothing will change in its calculations, whether Biden is at the top of the Democratic ticket or not.

鈥淧resident Trump will beat any Democrat on November 5th because he has a proven record and an agenda to Make America Great Again,鈥 co-campaign managers Chris LaCivita and Susie Wiles said in a statement.

Even if Biden is not the Democratic nominee, the Trump campaign believes the issues likely to decide the election will remain the same.

鈥淭he issues are the issues, and that鈥檚 what people care about,鈥 one adviser told CNN.

However, the reality may not be so clear-cut. Polling has shown a lack of enthusiasm around both the major parties鈥 presumptive nominees for president, and it鈥檚 unknown how a change could alter Democratic turnout or affect the opinions of swing voters. And while Democrats face a time crunch to make a decision before their August convention, so do Republicans, who have spent months building out a carefully crafted data operation, attack ads and general campaign infrastructure focused specifically on beating Biden.

As one Republican pollster put it, Trump would 鈥渞ather go with the devil he knows than the devil he doesn鈥檛 know.鈥

Behind the scenes, the Republican National Committee already had 鈥渞olling books鈥 of opposition research on prominent Democrats who could succeed Biden in 2028, Trump advisers told CNN, including Michigan Gov. Gretchen Whitmer, Arizona Sen. Mark Kelly, Pennsylvania Gov. Josh Shapiro and California Gov. Gavin Newsom, among others.

The books 鈥渁re constantly being updated, because, you know, they鈥檙e perpetual candidates, and they鈥檙e always running for something,鈥 one senior Trump adviser told CNN.

Still, two advisers to Trump said they would not be changing strategy or shifting research and plans until the situation with Biden had played out.

鈥淲e just don鈥檛 know what this looks like at the end of all of it,鈥 one of the advisers said. 鈥淲e鈥檙e not going to change anything until we know.鈥

Some Republicans had publicly floated, if not anticipated, a Biden exit from the race as the president鈥檚 physical decline became increasingly apparent. During the GOP presidential primaries, Florida Gov. Ron DeSantis and former South Carolina Gov. Nikki Haley made it a focal point of their campaigns, arguing that Democrats would replace Biden and Republicans couldn鈥檛 risk putting Trump up against a more youthful and energetic challenger.

Trump himself had broached the prospect, saying repeatedly that he didn鈥檛 think Biden 鈥渕akes it.鈥 In an interview nearly a year ago, Trump and conservative commentator Tucker Carlson opined on what would happen if Biden left the race.

After Carlson suggested Harris would replace Biden on the Democratic ticket, Trump predicted: 鈥淣ot really. I mean, I guess they鈥檇 have maybe a free-for-all. A lot of people say she has to remain for certain reasons. I don鈥檛 think that鈥檚 true actually. 鈥 I don鈥檛 think other people would stand for it.鈥

But in the aftermath of the debate, Trump鈥檚 team did not anticipate such lasting Democratic panic surrounding the viability of Biden to continue as the party鈥檚 presidential nominee. One Trump adviser told CNN the Democratic handwringing had been expected to blow over within a week.

Now, Trump鈥檚 team is scrambling to prepare for any outcome, including whether it may need to mount a new campaign focused on a different opponent.

鈥淓very Democrat who is calling on Crooked Joe Biden to quit was once a supporter of Biden and his failed policies that lead to extreme inflation, an open border, and chaos at home and abroad,鈥 LaCivita and Wiles said in their statement. 鈥淢ake no mistake that Democrats, the main stream media, and the swamp colluded to hide the truth from the American public.鈥

Republicans are now plotting how to hit Harris, with early discussions focused on her past statements defending Biden鈥檚 fitness to serve.

鈥淪he going to constantly be forced to answer a very simple question: Why were you hiding Joe Biden鈥檚 lack of mental acuity from the American people?鈥 a person close to Trump said.

Most people close to Trump continue to believe that a change is unlikely, citing the relative low name recognition of the prospective Biden replacements and the legal challenges of moving the president鈥檚 campaign war chest to a new candidate. Biden, too, continues to insist he isn鈥檛 going anywhere. In a defiant campaign call Wednesday, he told staff, 鈥淣o one is pushing me out鈥 and vowed to stay in the race.

鈥淚鈥檓 not leaving,鈥 he said, sources familiar with the call told CNN.

Efforts to keep Biden on the ballot may come from the right as well. The Heritage Foundation, a Trump-aligned conservative organization, has been readying for this moment since the spring and recently revealed a playbook to challenge attempts by Democrats to remove Biden from the ballot in certain states with statutory deadlines for naming nominees.

In a memo released last month somewhat presciently titled 鈥淐an they replace Biden if he freezes at debate,鈥 the organization singled out three swing states 鈥 Georgia, Nevada and Wisconsin 鈥 where Republicans could file lawsuits to challenge efforts by Democrats to change course.

Mike Howell, executive director of Heritage鈥檚 election oversight project, acknowledged that any winning case would heavily depend on the circumstances of a Biden departure.

鈥淭he timing is so key,鈥 Howell said.

Rick Hasen, an election law expert at UCLA, rejected the idea that Democrats would have any legal trouble putting forward a new name before Biden is even officially nominated.

鈥淚 don鈥檛 put any credence into it,鈥 Hasen wrote on his website. 鈥淛oe Biden is not the party鈥檚 nominee now, and states generally point to the major party鈥檚 nominee as the one whose name is on the ballot.鈥

CNN鈥檚 Betsy Klein and Kate Sullivan contributed to this report.