As Veterans Affairs Secretary David Shulkin battled last month to keep his job, his fate hinged in part on a once-obscure advocacy group backed by billionaire industrialists Charles and David Koch.

In the end, Shulkin's refusal to pursue greater outsourcing of health care for veterans - the top priority of the Koch-backed Concerned Veterans for America - further alienated him from the group's allies in the Trump administration and contributed to his ouster, according to officials familiar with the situation.

The VA secretary's fall underscores the growing clout that CVA is wielding in the Trump era through a national grass-roots network and sympathetic officials in the White House.

What began as a savvy political strategy - tapping veterans as a potent constituency and seizing on bureaucratic failures at the Department of Veterans Affairs to hammer the Obama administration - has transformed CVA into one of the most muscular arms of the conservative Koch network.

Since its formation seven years ago, the group has racked up major legislative victories and poured at least $52 million into campaigns and policy work, according to tax filings.

In a sign of its influence, President Donald Trump recently echoed a key talking point of the group on the need to expand VA's "Choice" program, which gives veterans access to private doctors. "We want them to have choice so that they can run to a private doctor and take care of it," the president said at a rally in Ohio the day after Shulkin's firing. "And it's going to get done."

Concerned Veterans for America is now positioned to shape the priorities of Trump's new VA nominee, Ronny Jackson, a little-known presidential physician with scant policy or political experience. And the group is gearing up to be a big player again in the congressional midterm elections, investing $3 million so far this cycle attacking vulnerable Senate Democrats as weak on veterans issues - with millions more likely to come.

But CVA is setting its sights even higher. In its most ambitious campaign yet, the organization said it is embarking on a long-term effort to transform some of the nation's most costly policy investments by remaking VA - the country's largest health-care system - and the financing of the nation's military. The group said it wants to cut what it views as wasteful defense spending, such as funding underused military bases.

Driving the organization is the stark libertarian philosophy of the network's founder, Charles Koch, who has long sought to curtail the reach of the federal government.

Patrick T. Fallon / Getty Images Charles Koch speaks during an interview with the Washington Post at the Freedom Partners Summit on Aug. 3, 2015 in Dana Point, Calif. Concerned Veterans for America has become one of the most muscular arms of the conservative Koch network. Charles Koch speaks during an interview with the Washington Post at the Freedom Partners Summit on Aug. 3, 2015 in Dana Point, Calif. Concerned Veterans for America has become one of the most muscular arms of the conservative Koch network. (Patrick T. Fallon / Getty Images) (Patrick T. Fallon / Getty Images)

"This isn't a one-year fight. This isn't a two-year fight. This is a fight that is going to extend beyond the Trump administration," said Dan Caldwell, CVA's executive director and a Marine Corps combat veteran who served in Iraq. "When a system isn't working well, it's not just wasting taxpayer money; it's hurting our warfighters."

CVA's critics - including the congressionally chartered veterans groups - acknowledge the need for some private care, but they argue that unfettered privatization would be costly and siphon resources from the VA system.

Ryan Gallucci, director of national veterans services for Veterans of Foreign Wars, said that CVA does not represent the views of veterans, noting that VFW members report in surveys that they are happy overall with VA health care, despite its challenges.

"What they report doesn't match up against what our members tell us," Gallucci said. He said he is worried that CVA's agenda would hurt veterans.

"The notion of giving them a card to take anywhere is, quite frankly, a cop-out," he said. "It becomes downright dangerous. You need someone coordinating their care."

The traditional advocacy groups, which have been the dominant representatives of veterans since World War II, view Concerned Veterans for America as an interloper driven by the views of its wealthy backers, not average veterans.

"They're a political lobbying firm," said Louis Celli, national director of veterans affairs and rehabilitation for the American Legion, the country's largest veterans group. "They're not a veterans organization. They're using veterans issues as a tool to push a political agenda."

In media interviews after his ouster, Shulkin blamed his removal on forces that would benefit from a diminished government health-care system for veterans.

"I just don't see privatization as a good thing for veterans," he told PBS's "NewsHour" the day after his dismissal. "I think those that are really sticking to a political ideology are doing this for other reasons, like financial reasons, [and] don't have the interests of veterans at heart."

Andrew Harnik / AP In this March 7, 2018, photo, Veterans Affairs Secretary David Shulkin speaks at a news conference at the Washington Veterans Affairs Medical Center in Washington. Shulkin is making it clear he was fired from his job amid conflicting claims from the White House. In this March 7, 2018, photo, Veterans Affairs Secretary David Shulkin speaks at a news conference at the Washington Veterans Affairs Medical Center in Washington. Shulkin is making it clear he was fired from his job amid conflicting claims from the White House. (Andrew Harnik / AP) (Andrew Harnik / AP)

As a politically active nonprofit organization, Concerned Veterans for America is not required to disclose the names of its donors. Koch officials declined to respond to the suggestion that the group's financial backers would profit from the outsourcing of veterans' care.

Koch officials noted that CVA never publicly called for Shulkin's firing. And they argued that the group should be credited for drawing national attention to bureaucratic failures that hurt veterans.

"Part of CVA's tremendous growth has been on delivering really good reforms at the VA," said network spokesman James Davis.

Concerned Veteransfor America was formed in 2011 as a nonprofit group named Vets for Economic Freedom Trust, and was seeded withnearly $2 million from Koch network donors, tax documents show.

In its early days, the organization presented itself as a full-service veterans advocacy group. But it also tackled issues outside the usual fare of veterans groupsto focus on touting conservative policies that were top agenda items of the Koch network.

Ahead of the 2012 election, founding president Pete Hegseth - now a Fox News contributor - argued that the issue that most worried veterans was the national debt.