WASHINGTON (AP) — President Donald Trump's selection of his White House doctor to run the massive Department of Veterans Affairs triggered concern Thursday among lawmakers and veterans groups about whether he has the experience to manage an agency paralyzed over Trump's push to expand private care.

Ronny Jackson, a Navy rear admiral entrusted with the health of the past three presidents, is a lifelong physician whose positions on privatizing operations in the second largest federal department and addressing ballooning health care costs are unknown. First named to the top White House post by President Barack Obama, he would be new to running a big bureaucracy if given leadership over a department of 360,000 employees serving 9 million veterans.

In a statement, Trump praised Jackson as "highly trained and qualified." But representatives of veterans aren't sold on the choice, or on Trump's decision a day earlier to fire VA Secretary David Shulkin.

"There is little that we know about Dr. Ronny Jackson's vision and qualifications," said Paul Rieckhoff, founder and CEO of Iraq and Afghanistan Veterans of America. "Our concern is whether President Trump was more interested in picking a secretary who would be politically loyal rather than someone who can work across the aisle to fix long standing problems of bureaucratic delay."

Similar doubts were expressed by Veterans of Foreign Wars, which praised Jackson's military background in a statement but pointed to a nominee biography devoid of "any experience working with the VA or with veterans, or managing any organization of size, much less one as multifaceted as the Department of Veterans Affairs." AMVETS echoed such sentiments.

"We look forward to a rigorous confirmation hearing," Rieckhoff said.

Montana Sen. Jon Tester, top Democrat on the panel that will consider the nomination, said he had yet to determine if Jackson "is up to the job."

It's not clear from Jackson's military service record how much, if any, management experience he has. His military assignments did not appear to include supervision over a large department or unit. His Navy biography says he deployed to Iraq with a Marine unit and served as the emergency physician in charge of resuscitative medicine for a trauma platoon.

Jackson joined the White House medical team in 2006 and is perhaps best known for his appearance before the press corps in January, announcing the results of Trump's first physical in a performance that showed he was quick-witted and unfailingly complimentary of Trump.

Marveling at the 71-year-old president's good health, Jackson opined, "It's just the way God made him."

A White House official said Shulkin himself had recommended Jackson for an undersecretary position at the VA in the fall, and Trump ultimately decided he was more comfortable with Jackson than with other top candidates. The official was not authorized to discuss personnel matters and spoke on condition of anonymity.

If confirmed by the Senate, Jackson would face immediate crises, like a multi-billion dollar revamp of electronic medical records now in limbo that members of Congress fear will prove too costly and wasteful, and a budget shortfall in the coming weeks in its private-sector Veterans Choice program.

Trump is seeking an aggressive expansion of the Choice program to make it easier for veterans to see private doctors outside the VA system at government expense, but proposals are stalled in Congress following a failed effort last week.

"We're going to have real choice," Trump said in Ohio. "That's why I made some changes, because I wasn't happy with it."

Jackson's nomination comes as Trump's new Cabinet nominees begin to pile up in the Senate. That is certain to stir weeks of confirmation battles this spring when senators, especially those running for re-election, may prefer to shift focus away from the changes at the White House.

None of the nominees, including the president's new picks for secretary of state and CIA director, is expected to sail to easy confirmation. The GOP-led Senate is narrowly divided 51-49 and Democrats — and some Republicans — are preparing to ask tough questions. Even though Congress has an otherwise slim legislative agenda before campaign season, prolonged confirmation fights could jam up the Senate and influence the election.

Pending Jackson's confirmation, Robert Wilkie, a former Pentagon undersecretary for personnel and readiness, is serving as the acting head of the VA.

Lawmakers said they needed to learn more about Jackson's record.

Republican Sen. Johnny Isakson of Georgia, chairman of the Senate Veterans Affairs Committee that will review the nomination, declined to indicate his support. He stressed that he looked forward to "meeting Admiral Jackson and learning more about him." Isakson, a moderate, has expressed skepticism in the past toward toward nominees who expressed strong views in favor of privatization.

Sen. Bernie Sanders, independent of Vermont and a former chairman of the panel, cautioned that Jackson would not be approved if he supported privatizing the VA. "Our job is to strengthen the VA in order to provide high-quality care to our veterans, not dismember it," he said.

Shulkin, a physician and the lone Obama administration holdover in Trump's Cabinet, was unceremoniously fired late Wednesday by Trump in a tweet. Shulkin had enjoyed support from Trump for much of his first year in the administration but support eroded last month after a bruising ethics scandal and political infighting at VA.

Dan Caldwell, executive director of the conservative Concerned Veterans for America, said the group is keeping an "open mind" about Jackson's nomination. Some of the names that had been in circulation for the post had previous ties to the group, which supports giving veterans greater access to private doctors outside the VA system.

"We'd like to hear more about his positions to reform and fix the VA," Caldwell said. "He has a very distinguished service record and it would be unfair to outright dismiss him — you have to be very professional to reach his rank."

A native of Levelland, Texas, Jackson, 50, graduated from Texas A&M with a degree in marine biology, then from medical school at the University of Texas Medical Branch.

He headed to the Navy, then in 2005 joined a 2nd Marines regiment. Jackson was deployed to Iraq as the physician in charge of resuscitative medicine for a trauma platoon, according to the White House.

Ned Price, a National Security Council spokesman under Obama, described the doctor as "the guy you always want to be around" because he's affable and funny. But Price said it was difficult to believe the nomination was unrelated to the "glowing assessment" of Trump's health that the doctor had provided.

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Associated Press writers Jill Colvin, Lisa Mascaro, Lolita Baldor, Zeke Miller, Jonathan Lemire, Catherine Lucey and Darlene Superville contributed to this report.