WASHINGTON (AP) — Former Veterans Affairs Secretary David Shulkin is blaming his sudden ouster from the Trump administration on "political forces" that he says are bent on privatizing the agency and putting "companies with profits" over the care of veterans.

Shulkin, the lone Obama administration holdover serving in President Donald Trump's Cabinet, blasted a "toxic" and "subversive" environment in Washington that made it impossible for him to lead. In a tweet late Wednesday, President Donald Trump fired Shulkin, who faced a mounting internal rebellion at VA and a bruising ethics scandal.

"As I prepare to leave government," he wrote in a New York Times op-ed Thursday, "I am struck by a recurring thought: It should not be this hard to serve your country."

Shulkin said he was undone by advocates of privatization within the administration.

"They saw me as an obstacle to privatization who had to be removed," he said. "That is because I am convinced that privatization is a political issue aimed at rewarding select people and companies with profits, even if it undermines care for veterans."

The issue of privatizing VA has been a political hot button since the 2016 campaign, when Trump pledged to aggressively expand veterans' access to private doctors outside the government-run VA system at taxpayers' expense in the wake of a 2014 scandal at the Phoenix VA medical center in which some veterans died while waiting months for medical appointments.

Major veterans groups and Democrats stand opposed to an aggressive expansion, seeing the effort as a potential threat to the viability of VA medical centers.

The firing comes after the VA's internal watchdog last month concluded that Shulkin had improperly accepted Wimbledon tennis tickets and that his then chief of staff had doctored emails to justify his wife traveling to Europe with him at taxpayers' expense.

But in the op-ed, Shulkin, a physician, claimed he had been "falsely accused" and blamed the "politically based attacks on me and my family's character."

Trump nominated White House doctor Ronny Jackson to replace Shulkin.

A White House official said Shulkin was informed of his dismissal by chief of staff John Kelly Wednesday afternoon before the president announced the move on Twitter. Shulkin's name was scrubbed from the Department of Veterans Affairs website soon after. Shulkin packed up his office and in response to a reporter's query late Wednesday dejectedly emailed: "Let's talk tomorrow — I just need tonight to myself."

By Thursday morning, he was making rounds with news media, pledging to continue speaking out" against those who seek to harm the VA by prioritizing their personal agendas.

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Associated Press writers Zeke Miller, Catherine Lucey and Jonathan Lemire contributed to this report.