After being blindsided by Donald Trump’s 2016 campaign, Democrats are preparing themselves for a variety of political scenarios in the next presidential election—including the possibility that Trump himself isn’t on the ballot. While the president already filed paperwork for re-election on the day of his inauguration, the Democratic National Committee has begun compiling opposition research on a number of high-profile Republicans with presidential aspirations that the organization views as likely to run in 2020, either against Trump or in his place. According to a Politico report, the list includes Ohio Governor and Trump antagonist John Kasich, Vice President Mike Pence, United States ambassador to the United Nations Nikki Haley, and Nebraska Senator and vocal Trump critic Ben Sasse, among others.

Of those contenders, Pence is probably the most formidable, and the most likely to run. The vice president’s machinations have fueled speculation that he isn’t content with the No. 2 job in Washington and is maneuvering himself for something more. (What is the vice presidency, after all, except a stepping stone to the real thing?) In an unprecedented move earlier this year, Pence launched his own political-action committee, while also building relationships with top Republican donors. Pence’s team has repeatedly rebuked reports about his potential ambitions, but Democrats aren’t taking any chances: the D.N.C. is already digging into Pence’s record in preparation, as is the Democratic opposition super PAC American Bridge 21st Century.

The next most likely Republican to be on the ballot in 2020, after Trump and Pence, is Kasich, whom the D.N.C. has tasked a team of two dozen researchers with investigating, building on the opposition research from last year’s election. The Ohio governor has been harshly critical of Trump and has stopped short of saying he won’t make another bid for the White House in 2020, though he has said he wouldn’t take on Trump. John Weaver, one of Kasich’s political advisers, sought to tamp down the rumors, telling Politico, “I think the Democrats would be better served coming up with a better economic policy rather than planning to rely on Trump’s unpopularity.” Haley and Sasse, both viewed as rising stars within the G.O.P., have also been floated as potential 2020 candidates.

It is unusual for there to be this sort of speculation just seven months into a new administration, but Trump is no usual president. “Needless to say, there is no historical precedent for this kind of challenge to a sitting president this early in his term. I do think it’s important to begin to have these discussions, if for no other reason than to make it clear that there remain Republicans unstained by Trump’s presidency,” Charlie Sykes, a veteran influential conservative radio host based in Wisconsin, told Politico.

Others say the Democratic effort is entirely misguided. As Tom Rath, a longtime Republican strategist in New Hampshire who advised Kasich in 2016, explained to Politico, for a Republican challenge to Trump be seriously considered, “the circumstances that would compel or permit such a change would have to be so remarkable, so sweeping, so unprecedented that any oppo research on a particular candidate would be rendered moot by the very circumstances that occasioned the change.” He added, “I would think, if I were a Dem, I would really want to run against Trump in [2020] rather than any one else.” But that said, even Trump’s team is reportedly keeping an eye on Kasich along with a field of likely Democratic candidates.