According to Sims, the discussion he describes took place at the White House in April 2017, as Trump prepared to make a very long-distance video call from the Oval Office to the International Space Station. Peggy Whitson, a NASA astronaut, had broken the American record for the longest time spent in space, and the president was going to congratulate her.

About 10 minutes before the call, which was live-streamed to the public, Trump “suddenly turned toward” Robert Lightfoot Jr., the acting administrator, and asked him, “What’s our plan for Mars?”

Lightfoot explained that NASA hopes to put people on the planet by the 2030s.

“But is there any way we could do it by the end of my first term?” Trump asked.

Sims writes that a fidgeting Lightfoot tried to explain some of the technical challenges of a Mars mission.

Trump was undeterred: “But what if I gave you all the money you could ever need to do it? What if we sent NASA’s budget through the roof, but focused entirely on that instead of whatever else you’re doing now. Could it work then?”

Lightfoot said he was sorry, but no. The interaction, according to Sims, left the president “visibly disappointed.”

NASA directed my questions about this exchange to the White House. The White House did not respond to multiple requests for comment.

The call with the International Space Station began soon after. The question of Mars seemed to have stuck with Trump and, apparently unsatisfied with Lightfoot’s answer, the president decided to ask Whitson, the astronaut.

“What do you see a timing for actually sending humans to Mars? Is there a schedule? And when would you see that happening?” Trump asked.

“Well, I think as your bill directed, it will be approximately in the 2030s,” Whitson replied.

“Well, we want to try and do it during my first term or, at worst, during my second term,” Trump said. “So we’ll have to speed that up a little bit, okay?”

“We’ll do our best,” she said, with a laugh.

At the time, the brief exchange came off as a mix of enthusiasm and confusion on Trump’s part. “Based on how he said it, it seemed like it was a tongue-in-cheek comment,” a White House spokesperson told me then. “I wouldn’t really look beyond that.” But according to Sims’s account, the president was apparently serious about getting to Mars during his presidency.

To echo Lightfoot, that’s not possible. The money would certainly be welcome, of course. (Congress would also have to approve it.) What government agency would turn down presidential support for a budget influx? Especially NASA. During the Apollo era, the agency’s annual funding accounted for 4.5 percent of the federal budget. It shrunk to less than half a percent by the end of Richard Nixon’s term, and has remained there since.

But cash is no substitute for time, and space travel is difficult to rush, even with Cold War tensions hovering menacingly in the background. Eight years elapsed between John F. Kennedy’s declaration to go to the moon and Neil Armstrong’s first steps on the lunar surface, and several Americans died in the effort to get there.