President Trump steps off Air Force One after arriving in St. Louis on March 14, 2018. (Evan Vucci/AP)

More than a year after entering the White House, President Trump still has not selected his top science and technology adviser, leaving unfilled a critical policy post that guides the administration on issues as varied as artificial intelligence,  climate change and cancer research.

While the White House maintains that it is unconstrained in its work — and has staffed up to tackle such challenges as closing the country’s Internet-access gaps — the vacancy still troubles policy experts, who believe that Trump would be best served by someone who could double as an emissary to the academic and engineering worlds.

“Symbolically, it signals science and technology is at the table in the administration's policymaking,” said Kumar Garg, who was an innovation policy aide under President Barack Obama. “But also substantively, because the science adviser is the principal who gets invited to senior strategy meetings ... on critical topics like biosecurity, cybersecurity, how do we make sure America remains competitive against China and Russia in emerging technology.”

Technically, the White House has two major science and technology posts. The first is the director of the Office of Science and Technology Policy, which has a broad remit that includes coordinating the country’s vast federal research budget. The second is the assistant to the president on science and technology, a title that is supposed to afford its bearer access to the person occupying the Oval Office. Often, those roles are held by the same person, and under Obama, the responsibilities fell to John Holdren for eight years.

Since Holdren's departure, the posts have remained vacant. But Trump's aides have actively sought new leadership for months. One of the candidates under consideration is Kelvin Droegemeier, an expert in extreme weather and meteorology from the University of Oklahoma, according to three people familiar with the president’s thinking but not authorized to speak on the record. The people said others are in the running.

The White House and the OSTP declined to comment for this article. Reached this week by email, Droegemeier declined to comment.

Under Trump, the White House generally has operated with a much smaller complement of science and technology staffers than it did under Obama. The OSTP counts about 50 aides today, compared with the roughly 130 Obama had tapped before leaving office. Some of that is by design, as Trump has sought to scale back the size of government. But some of it is the result of the president’s at-times icy relationship with liberal-leaning Silicon Valley, where top technology executives and engineers — experts who could have formed his policy ranks — have become some of his biggest public critics.

Among Trump's tech policy advisers is Michael Kratsios, a former aide to venture capitalist Peter Thiel who joined the administration in its early days to serve as deputy chief technology officer. The White House has retained other policy staffers recently who focus on artificial intelligence and education, and at the OSTP, they have advanced some early initiatives that have satisfied tech giants in Silicon Valley and beyond. That includes efforts to speed up the arrival of 5G, the next generation of ultrafast, wireless Internet service for smartphones and other devices.

At the same time, critics have bristled as the president has proposed multiple budgets that would slash federal programs that seek to combat global warming, which Trump described in 2013 as a “hoax.” And Trump’s decision last year to withdraw the United States from a worldwide carbon-reduction treaty, the Paris climate accord, drew outrage from hundreds of business leaders in technology and other industries.

For that reason, veterans of the White House maintain that Trump needs a full-time, senior expert with the same sort of access afforded to his top aides in defense and economics.

“I’m happy they are staffing up,” said Kei Koizumi, an assistant director at the OSTP under Obama who is a visiting scholar at the American Association for the Advancement of Science.

But, Koizumi added: “I remain concerned for them to be fully effective. There's no substitute for leadership that can back their work and make sure they are listened to.”

If the White House proceeds with Droegemeier, it would add to its ranks a highly experienced meteorologist with government experience. He has served as Oklahoma’s secretary of science and technology, and he aided the U.S. government’s National Science Board under Presidents George W. Bush and Obama.

Publicly, Droegemeier has advocated for sustained federal research spending, even as Trump at times has pursued cuts. Meanwhile, Droegemeier has come to the defense of at least one of Trump's current nominees, Rep. Jim Bridenstine (R-Okla.), whose views on climate change prompted Democrats to block his nomination to lead NASA.

Droegemeier could be nominated to run the OSTP, or he could be appointed to serve solely as assistant to the president for science and technology. The latter post, if it is uncoupled from the OSTP, doesn’t require Senate confirmation. In that case, Trump might be spared periodic, high-profile showdowns with his Democratic critics on Capitol Hill, who are itching to challenge him on global warming and related debates.

Previously, the White House considered turning the OSTP over to Jim O’Neill, a Silicon Valley investor who also has ties to Thiel, according to two of the three people who spoke off the record. O’Neill is no longer in the running, they said.