As the impeachment inquiry against President Trump continues its march through Congress, questions are churning around his secretary of state, Mike Pompeo.

For example, did he know, as witnesses testified before House investigators, that President Trump sought political favors from Ukraine in exchange for millions in U.S. assistance? Why did he take days to reveal he was on the now infamous July 25 call between Trump and Ukrainian President Volodymyr Zelenskiy? And does he believe allies of the president who — despite the findings of the intelligence community — claim that Ukraine, not Russia, interfered in the 2016 election?

For Pompeo, the questions surrounding what he knew about the Ukraine affair, and when, reflect the outsized role he has assumed as one of the president's most influential advisers. It is a position that just four years ago would have seemed unlikely for Pompeo, yet underscores the extent to which the political fortunes of the onetime Trump critic have grown increasingly tied to the president.

From West Point to Kansas

Pompeo's path from a West Point graduate to the nation's chief diplomat is all the more remarkable considering his early resistance to Trump. He supported Florida Sen. Marco Rubio during the 2016 Republican primary, and in a speech ahead of that year's Kansas caucus, likened Trump to an autocrat.

"You know, Donald Trump the other day said that 'if he tells a soldier to commit a war crime, the soldier will just go do it.' He said, 'They'll do as I tell them to do.' We've spent seven-and-a-half years with an authoritarian president who ignored our Constitution," Pompeo said. "We don't need four more years of that."

It was a criticism steeped in Pompeo's background not just in the military, but also the law.

Pompeo grew up in conservative Orange County, California, and after high school, attended West Point, where he finished first in his class in 1986. After graduation, he became an Army commander in Germany before returning to the U.S. to attend Harvard Law School. At Harvard, he was an editor of the Harvard Law Review.

Law school took him to a prestigious Washington, D.C., law firm, Williams & Connolly, but in 1997, he left the firm to open an aircraft-parts manufacturing firm in Kansas with three of his West Point classmates. Among their investors was the venture capital fund of the billionaires and Republican mega-donors Charles and David Koch.

In 2010, Pompeo left his business career to run for Congress. Jim McLean, managing director of public radio's Kansas News Service, says Pompeo's entry into politics came as the Koch brothers' own forays into politics were growing.

"The Koch brothers really got politically active when he was getting into politics," McLean said.

The Benghazi hearings

With his election in that year's midterm elections, Pompeo joined a wave of 87 Republicans that helped propel the GOP back into the House majority. But it was not until the 2014 House inquiry into the 2012 attack on an American diplomatic post in Benghazi, Libya, that Pompeo became a name in national news, according to McLean.

"He was pretty much a nonentity, politically speaking, on the national scene up to that point, and frankly, he was overshadowed even here in Kansas politically," said McLean. "But those Benghazi hearings, he really did take on a lead role as inquisitor. And there was, you know, some very famous confrontations with Hillary Clinton during those hearings."

Nancy McEldowney, a career diplomat and former director of the Foreign Service Institute, said Pompeo was among a cadre of Republicans who pushed the attack into becoming "the kind of domestic controversy that it was turned into."

"They refused to join the consensus with the congressional investigatory committee and wrote their own addendum," said McEldowney, who now teaches at Georgetown University. "They talked about a State Department seemingly more concerned with politics than protecting its own people."

By 2017, Trump had won the White House and Pompeo's work on the Benghazi committee had helped make him a leading voice on foreign policy in the Republican Party. Despite Pompeo's earlier criticisms, Trump picked him to be his first CIA director, a position he held for a little over a year. He often personally delivered the daily security briefing to the president.

In March 2018, Trump nominated Pompeo to succeed Rex Tillerson as secretary of state. Tillerson had left key posts unfilled at the department, alienating many career foreign service officers. At the time, McEldowney said, many State Department personnel were heartened by the nomination.

"People thought at least his close relationship with the president and his experience as a military officer would help his leadership of the State Department," said McEldowney. "So initially, there was a positive feeling, a hopefulness that Pompeo would turn around the destruction of the Tillerson time."

At his confirmation hearing for the post, Sen. Tom Cotton, an Arkansas Republican and Pompeo ally, said, "When Mike Pompeo speaks, the world will know the secretary of state speaks for the president."

Questions around Ukraine

But the honeymoon was short-lived. From his perch as secretary of state, Pompeo has emerged as a key focus in the ongoing Ukraine investigation. More than two months after Democrats launched an impeachment inquiry into the president, critical questions remain about how Pompeo disclosed that he was on the line for the July 25 call between Trump and Zelenskiy that became the focus of the whistleblower complaint that sparked the inquiry.

When Pompeo was asked about the call by reporters on Sept. 26, he said he still had not fully read the partial transcript of the call released by the White House one day earlier.

"I read the first couple of paragraphs and then got busy today," Pompeo said. "But I'll ultimately get a chance to see it. If I understand it right, it's from someone who had secondhand knowledge."

It wasn't until almost a week later that he acknowledged he was on the call.

Peter Roskam, a former Republican congressman from Illinois who served with Pompeo, said he doesn't believe the secretary misled the public.

"I'm convinced that he was forthright and direct with the American public and he's been forthright and direct I think at every turn up and down," said Roskam.

Questions have also been raised about why Pompeo did not defend U.S. diplomats from political attack, beginning with Marie Yovanovitch, who was relieved from her post as U.S. ambassador to Ukraine this spring after becoming a target of criticism among the president's allies. In testimony before impeachment investigators, diplomats described the ouster as part of an effort by the administration to exert pressure on Ukraine in exchange for political investigations.

"He allowed Yovanovitch to be first be smeared" and then removed from her post, McEldowney said of Pompeo. "He did not stop that. And that has had such a poisonous impact on other diplomats throughout the service."

While the president has the prerogative to set foreign policy, she said, "It's one thing to have powers that you can execute. It's another to abuse them."

As the impeachment inquiry approaches a potential trial in the Senate, Democrats will want Pompeo to testify as one of the aides closest to the president and his policy toward Ukraine. Pompeo was subpoenaed by the House Intelligence Committee, but Democrats on the committee say he has not complied with their requests.

Susan Glasser, who recently profiled Pompeo for The New Yorker, said lawmakers have no shortage of questions for Pompeo.

"What did he know about the withholding of nearly $400 million in congressionally appropriated aid to Ukraine? When did he know it? What direct conversations, if any, did he have with the president? Rudy Giuliani says that everything he did was carried out with the knowledge of the State Department. Is that, in fact, the case?"

A return to Kansas?

While Pompeo has not testified in Congress about the Ukraine controversy, he has had made time to do interviews with local Kansas media. This has fanned speculation that Pompeo plans to leave Washington and run for a senate seat in Kansas, where McLean of the Kansas News Service says impeachment, Ukraine and quid pro quo sound a long way's away.

"The initial stories that have been written about how Kansans would view Pompeo's alleged role in whatever took place relative to Ukraine and the cover-up and all those issues, so far at least people seem to say, 'Hmm, well, you know, that's what's happening in D.C.' Nobody is really sure to what extent that would affect a candidacy here in Kansas."

At this week's NATO summit, President Trump told reporters he may ask Pompeo to return to Kansas to try to win a seat that would help Republicans keep control of the Senate. As Glasser pointed out, Pompeo has tied his political fortunes to Trump.

"His power and his currency comes from being as close as he can, allied with Trump and his policy preferences and Pompeo has really defined himself as there never ever being any daylight between himself and Trump," said Glasser.

But it's precisely Pompeo's closeness to the president that makes him a crucial figure in the investigations and impeachment to come.

This story was produced and edited for broadcast by Peter Breslow and Martha Wexler.