The Apollo moon landings represent a milestone in human history, albeit one driven by the Cold War rivalry with the Soviet Union and the demonstration of American technological capability in a global struggle for hegemony. There have since been four major attempts to go “back to the moon — and on to Mars,” including the Trump administration’s initiative. Those attempts to return to the moon after Apollo did not yield success, but they are nonetheless instructive in considering how the current effort may unfold.

Even as the Apollo program approached completion, the then-new Nixon administration chartered a Space Task Group on Feb. 13, 1969, under the chairmanship of Vice President Spiro T. Agnew, to plot a course for the post-Apollo space program. The group’s report reflected NASA’s desire for a space station, a reusable space shuttle, a moon base and a human expedition to Mars, but it proved politically untenable. Nixon responded March 7, 1970, that he would not approve NASA’s wish list and instead declared that the nation “must also recognize that many critical problems here on this planet make high priority demands on our attention and our resources.”

Ultimately, the problem was that the price tag for the STG recommendations was too high for Nixon. He did not see the need to again spend the amount of money — or perhaps ultimately even more — that had been necessary to fuel America’s trips to the moon in Project Apollo. He chose instead to retrench and approved only the space shuttle program in 1972, since it was the sole project NASA had put forward that did not require the other pieces to support it. (NASA eventually flew the space shuttles 135 times between 1981 and 2011.)

NASA thus cheered on July 20, 1989, when President George H.W. Bush announced on the steps of the Smithsonian Institution’s National Air and Space Museum the formation of the Space Exploration Initiative that would return Americans to the moon by 2000, establish a lunar base and then reach Mars by 2010. The price tag for this effort was estimated at a whopping $700 billion over two decades.

Congress immediately reacted negatively: In votes for fiscal year 1991 NASA funding, the SEI proposal was virtually zeroed out, despite lobbying from Vice President Dan Quayle (as the head of the National Aeronautics and Space Council, an advisory group to the president). Although Bush castigated Congress for not “investing in America's future,” members believed such a huge sum could be better spent elsewhere. “We're essentially not doing moon‑Mars,” then-Sen. Barbara Mikulski, D-Md., bluntly declared.

With his support of SEI, Bush had attempted to bring the space program full circle back to the early 1960s, but without the complementary elements that had made Kennedy's Apollo decision viable — that is, the crisis atmosphere that fostered the political will to do something spectacular, a favorable economic and technological climate and solid political support.

Subsequently, in February 1993 — looking for ways to cut the federal budget and thereby ease the federal deficit — the then-new Clinton administration announced that SEI did not fit into its plans for the space program. The NASA administrator at the time, Daniel S. Goldin, said that the agency was not, however, giving up on the idea of sending Americans back to the moon and on to Mars, but simply “putting it off until we’re ready and the nation is able to afford it.” The fiscal year 1994 budget contained virtually no funding for SEI; the effort died a quiet death.

Finally, the tragic loss of the space shuttle Columbia on Feb. 1, 2003, signaled the beginning of an important debate about the future of American human spaceflight. President George W. Bush announced a “Vision for Space Exploration” on Jan. 14, 2004, that called for humans to return to the moon and go on to Mars during the next 30 years. In support of this goal, the Bush administration announced that the nation would: Implement a sustained and affordable human and robotic program to explore the solar system and beyond; extend a human presence across the solar system, starting with a human return to the moon by the year 2020, in preparation for human exploration of Mars and other destinations; develop the technology, knowledge and infrastructure to explore and to support decisions about the destinations for human exploration; and promote international and commercial participation in space exploration.

In doing so, the president called for completion of the International Space Station and retirement of the space shuttle fleet by 2010. NASA did not quite meet that target, but it did retire the shuttle in 2011. The funding that had been spent on the space shuttle — $3 billion to $5 billion per year — was then reinvested in commercial firms resupplying the International Space Station, and in the development of a new deep space launcher that would make possible the exploration of the moon and beyond.

The new mechanism envisioned to carry out the second Bush’s “Vision for Space Exploration” became the Constellation Program, and incorporated a presumed reuse of as much of the existing space shuttle technology, a new Ares I crew launch vehicle and the Ares V cargo launch vehicle, would provide the heavy lift capability necessary to journey back to the moon or to go beyond. Despite NASA’s valiant efforts, adequate funding for this endeavor never arrived and, by the time that President Barack Obama took office in January 2009, the “Vision” was all but gone because of bureaucratic and funding problems.

The new president canceled Constellation. Any return to the moon — not a priority in the Obama administration — would then have to rely on the nascent Space Launch System, a heavy lift rocket inaugurated in 2010 that has yet to fly nearly a decade later.

These four attempts to return to the moon have one overriding reason for their lack of success: None of them garnered the political support, translated into public dollars, sufficient to achieve the goal. Of course, the investment in Apollo resulted from its perceived central role in combating the Soviet Union in the Cold War; the moon race was a central battlefield in that 40-year geopolitical struggle. The protagonists of that war knew, both in the 1960s and now, that the future belongs to the civilization that advances science and technology. Apollo was a demonstration of that reality, and one that was obvious to all the nations of the world.

Americans have had several bites of the lunar apple since Apollo, without the same results. We could have sent humans back to the moon, and even to Mars; but, like Apollo, it would require a national mobilization that has not been present in any of these efforts.

Success in the current Trump administration’s initiative to go to the moon and on to Mars would require a difficult decision to accept additional political risk and also to expend greater funds in its accomplishment for at least a five-year period. Using Apollo as a model — addressed, as it was, to a very specific political crisis relating to U.S.-Soviet competition — anyone seeking to mount a major human space exploration must ask a critical question: What political, military, social, economic and cultural challenge, scenario or emergency can they envision to which the best response would be a national commitment on the part of the president (and other elected officials) to support a 25-30 percent increase to the NASA budget for more than a decade? In addition, would politicians be willing to shoulder the risk of perhaps more failures than successes, and possibly loss of life in these efforts?

Absent a major surprise that would change the space policy and political landscapes, I doubt that America’s elected leaders will support an aggressive, long-term, and expensive effort to return to the moon — and go on to Mars — any time in the near future. The question that remains is whether any other country might answer those questions differently than we do.