Make America great again. Like most effective slogans, President Trump’s campaign motto can mean different things in different contexts. Viewed in a hopeful light, it could mean, “Bring back factory jobs displaced by automation and outsourcing.” Considered another way, it could mean, “Return to sanctioned discrimination, wage disparity and exclusion.” In a more charitable reading, it could mean, “Bring back a spirit of exceptionalism” — the sort that sparked Americans to invent airplanes and national parks and mass-produced cars and a government program to land humans on the moon.

Trump’s inaugural address nodded to this spirit. In addition to alluding to those faded factories and calling for patriotism as a tool against prejudice, Trump promised a future in which we are “ready to unlock the mysteries of space.” If Trump wants to do this, and to stimulate not only jobs but also a sense of awe and adventure, he could point the country toward Mars.

“Why is space so exciting? I think it brings out the best in us,” said W. Henry Lambright, a political scientist at Syracuse University and author of a book called “Why Mars.” “There’s something about space that captures the imagination that other fields don’t. It lifts people.”

Now is as good a time as any to give the country that lift.

Since the 1960s, Mars exploration has either been conducted by robot surveyors or confined to opaque dreams of human visitors. The first path has been an unqualified success. Humans have sent twenty-odd spacecraft to Mars, and uncrewed ships have uncovered many of the red planet’s secrets. NASA’s robotic missions have been following water, which suggests a habitable history, and have found plenty of evidence that Mars was once balmy and damp. Robotic orbiters and planned landers from Europe, Russia, China and India (none landed successfully, save for one Russian lander that lasted only 20 seconds on the planet’s surface) have been trying to understand Mars’s atmosphere and to look for life.

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But no nation has embarked on the second path. None has designed a rocket that could get humans to Mars, let alone launched a mission with a budget and a deadline. American leaders have offered vague plans, all of which have stalled. None has been as concise or as frank as John F. Kennedy was when he set a date by which we would land on the moon.

In a speech on July 20, 1989, two decades after Neil Armstrong and Buzz Aldrin met that deadline, President George H.W. Bush called for the construction of a new space station and a 10-year plan culminating in a mission to Mars. A subsequent NASA review panel said this would cost $500 billion, so the plan faltered and was quietly shelved. President Bill Clinton committed to finishing what became the International Space Station, but by 1996, the administration’s National Space Policy no longer included human exploration beyond Earth orbit.

In 2004, President George W. Bush proposed the Constellation program, which called for Americans to return to the moon by 2020 and reach Mars later. President Barack Obama canceled it, only to plan a mission to an asteroid as a stepping stone on a nebulous “Journey to Mars.” NASA officials continue to discuss this journey, even though there are no firm plans or timelines.

With inconsistent planning from one administration to the next, the nation has never had any plans for Mars that approach the scale of the Apollo program that took us to the moon, Lambright said.

“The moon program looks more and more like an astounding aberration in the American political context,” he said. “The space station does show it’s feasible to have a long-term program, but it has to be maintained by a sequence of presidents and a sequence of NASAs. And that’s the dilemma.”

Mars enthusiasts say things are looking up, however.

On Feb. 17, the Senate passed a NASA transition bill defining the agency’s goal as enabling “a capability to extend human presence, including potential human habitation on another celestial body” and to build an exploration program that can “achieve the long-term goal of human missions near or on the surface of Mars in the 2030s.” The earliest the House can take up the bill is Feb. 27, when lawmakers return from recess.

The bill also directs NASA to re-examine whether it’s possible to use the Orion spacecraft, which is still under development and would likely be the vehicle that takes humans to Mars, for missions to the International Space Station.

Assuming a timeline of about a decade and a half to build a rocket and send a ship to Mars, humans could reach the planet in the early 2030s, said Ellen Stofan, NASA’s former chief scientist. In testimony last week at a congressional hearing discussing NASA’s future, she said that a human mission in Mars orbit in 2032 — a favorable year for a Mars trip because Earth and Mars will be closer together — is “an achievable plan.”

“That is the plan NASA has started to work toward,” Stofan said in an interview, adding that a redirection to the moon would slow things down.

The transition bill is notable for containing such comprehensive Mars language, said Chris Carberry, the CEO of an advocacy group called Explore Mars. He said America in 2017, from Congress to private industry, offers unprecedented support for a Mars mission. Boeing, Lockheed, Aerojet Rocketdyne and, most ambitiously, SpaceX have announced Mars spacecraft concepts.

“Among the public, it’s really not even a race. Everything seems to be Mars these days,” Carberry said, pointing to a slew of popular movies, TV series and books.

Trump may have alluded to space in his inaugural address, but he has not yet appointed a NASA chief, nor anyone to lead the White House Office of Science and Technology Policy, so his plans are still unknown. The Trump administration declined to comment on these appointments or the president’s space policy.

Whether the journey will detour to the moon or an asteroid before reaching Mars, the problem is one of motivation (read: funding), not possibility, said Roger D. Launius, who served 12 years as NASA’s chief historian and 14 years as the Smithsonian Air and Space Museum’s space historian before retiring in January.

“Everybody likes this stuff, but nobody wants to pay for it,” he said.

As Launius sees it, humans have five principal reasons for flying in space. National security is first, followed by scientific enterprise. Third is capitalism — can you make a buck by building rockets? Ask Elon Musk in a couple more years. Fourth: Geopolitics. This is distinct from national security in that it’s about prestige and global standing, not just espionage. Geopolitics was the main reason we went to the moon. Fifth is the most fun or most ridiculous reason, depending on who you ask: Because it’s there.

“Astronauts love to say this kind of stuff. It’s human nature to explore, to climb the highest mountain, and at some level, that’s probably true. There’s a flip side of that, the dark side of this ethereal statement, which is, ‘If we don’t get off this planet, we’re gonna die,’” Launius said. The sun will eventually swell into a red giant and consume the Earth, after all. “But no member of Congress will make a decision to fund a program because of an event billions of years in the future. We can’t even get them to acknowledge threats that are much more imminent.”

Musk points to both adventure and self-preservation as his motivating factors. He unveiled his Mars plans last fall at a gathering of the International Astronautical Federation, a group founded during the Cold War. He said his mission is to minimize existential risk, carry forward the light of consciousness, and build a sense of adventure.

“The probable lifespan of human civilization will be much greater if we are a multi-planetary species,” he told the audience. “The argument I find most compelling is it would be an incredible adventure. Life needs to be more than solving problems every day. You need to wake up and be inspired.”

But inspiration is a hard sell. In Carberry’s view, the case for Mars is manifold, but it’s hard to nail down.

“There is not that single national security reason,” he said. “I think people understand it is good for the U.S. to remain a leader in the technologies that enable us to get to Mars; you can work that argument in. It’s just not as straightforward as, ‘Go to the moon to beat the Soviet Union.’”

In the 1960s, it was pretty straightforward. The setting for the moon landings was a hemisphere in crisis. Kennedy brought his moon shot to Congress on May 25, 1961, just five weeks after the failed Bay of Pigs invasion. Kennedy, Launius said, was trying to change the subject.

By 1962, members of Congress were decrying the increase in spending dedicated to the space race, Launius said. In September 1963, a year after the Cuban Missile Crisis and in the midst of a growing rapprochement with the Soviet Union, Kennedy addressed the United Nations to call for a joint American-Soviet moon mission. He was partly looking ahead to the 1964 election and worrying that Republicans would hang the expensive and unproven Apollo program around his neck. Reaching out to the USSR would not only serve as an olive branch, but it would also help underwrite the mission. Here’s a transcript of his speech.

Why should the United States and the Soviet Union, in preparing for such expeditions, become involved in immense duplications of research, construction and expenditure? Surely we should explore whether the scientists and astronauts of our two countries — indeed of all the world — cannot work together in the conquest of space, sending some day in this decade to the moon not the representatives of a single nation, but the representatives of all of our countries.

Kennedy directed the NASA administrator, James Webb, to develop a roadmap by January 1964 for bringing the Soviets into the Apollo program, Launius said. But this remarkable offer of cooperation fell apart after Kennedy’s assassination in November 1963. The space race became an emblem of the martyred president’s vigor and promise, and President Lyndon Johnson’s administration eagerly took up where Kennedy had left off. (There is a reason NASA’s mission control center is named for Johnson.)

It’s fun to consider counterfactual histories, but of course they are unknowable. One thing is almost certain, however: If NASA and the Soviet space agency had joined forces, Apollo would have happened on a different timeline. Freed from the sense of urgency brought on by the space race, NASA would have been able to slow down, do things differently, take fewer risks.

A Mars mission would be extraordinarily expensive and risky, and it’s unclear what benefits such a mission would bring. It’s also unlikely that any one space agency (or private company) could pull it off alone, which means the Russian or Chinese space agencies would probably be involved. No wonder progress has been slow.

“What crisis event, what trigger mechanism — use the term of your choice — would be one in which the president of the United States, Congress as a group, the American people as a majority, say the answer to that crisis would be to undertake a human mission to Mars?” Launius said. “I can’t think of one.”

Today, NASA is among the most revered agencies in America. About three-fourths of Americans view NASA favorably; among federal agencies, it’s second in esteem only to the Centers for Disease Control and Prevention, according to a 2013 Pew Research Center survey. But 30 years after the first moon landing, just 39 percent of Americans agreed that “the human race accomplished its single greatest technological achievement of all time by landing a man on the moon,” according to a 1999 Gallup poll. And it was hardly popular at the time. Throughout the 1960s, more than 40 percent of Americans opposed government-funded trips to the moon. At only one point, in a Gallup poll in October 1965, did more Americans favor continuing human lunar exploration than oppose it.

Part of the reason may be that the nation had much to grapple with at the time. Project Apollo infused NASA with cash and media attention during an era when black Americans were commonly barred from voting, were frequent targets of violence, and were suffering innumerable indignities. In February 1971, as Apollo 14 thundered off the launchpad, 200 black activists marched from Daytona Beach to Cape Canaveral to protest spending billions on a mission to “get some moon rocks.” They were protesting not the space program itself, but “our country’s inability to choose humane priorities,” said Southern Christian Leadership Conference leader Hosea Williams. And they were not the only ones to consider space exploration a low priority. In late 1965, The New York Times reported on a poll showing that Americans in six cities thought issues like anti-poverty programs and “Medicare for the aged” were of higher importance than space exploration, according to a 2003 research paper by Launius. Civil disorder, campus unrest, inflation and Vietnam also dominated the headlines in the mid-1960s and early 1970s.

“Most Americans seemingly preferred doing something about air and water pollution, job training for unskilled workers, national beautification, and poverty before spending federal funds on human spaceflight,” Launius wrote. “One must conclude … that the United States undertook and carried out Apollo not because the public clamored for it during the 1960s, but because it served other purposes.”

Modern polling suggests a similar theme. Carberry, of the Explore Mars advocacy group, commissioned a poll in 2013 during a federal budget fight. Americans were largely misinformed about how much federal money goes toward space exploration, the poll found. But when they were told that NASA receives a small fraction of the federal purse, their support for NASA and possible Mars missions grew, Carberry said.

“When they realize it’s a tiny part of the budget, and it’s not risking the solvency of Social Security or other social programs, it removes the guilt. They can support going to Mars,” Carberry said. But this support is not unqualified. A 2005 Gallup poll found that 58 percent of Americans opposed setting aside money for an attempted Mars landing, while 40 percent were in favor. The survey also revealed an interesting age split: 47 percent of adults under age 50 supported a mission to Mars, compared with 31 percent of people 50 and older.

Though the Explore Mars organization has an admittedly pro-Mars agenda, poll data shows that NASA, if not any of its specific programs, remains popular. A 2015 Pew survey showed 68 percent of Americans have a favorable impression of NASA, compared with 17 percent who have an unfavorable impression, and the numbers are similar across party lines. Gallup polls conducted periodically since 1978 show a similar trend, according to Launius, who adds that this disconnect in how people feel about NASA’s budget compared to the organization itself has shown up in polls for decades. There has always been a gap between Americans’ love of space and their willingness to pay for its exploration.

I asked Launius, who describes himself as a “cadet” and says he would love to see people walk on the red planet, if Mars could help make America great again.

“When did America stop being great? Is NASA representative of what suggests America is indeed great? One could make that case,” he said. “You could make that same argument with our robot explorers, our surrogates that have been to every planet in the solar system and beyond. We have learned enormous things about our place in the universe because of that. The question is, will most of the public accept that as a great thing as well? Or do you have to have bootprints on Mars, and the rest of the stuff doesn’t count?”

Launius said he doesn’t have the answer. That’s a question for the public, and for the new president, and for the ages.