President Obama does not envision defeating ISIS during his remaining time in office, the White House said Thursday, as administration officials counseled patience during a prolonged “degrade phase” of a strategy they maintain is accomplishing its goals.

While critics on Capitol Hill this week urged the White House to revamp the U.S. strategy to combat ISIS in the wake of the militants’ territorial gains in Ramadi, Iraq, and in Syria, the administration insisted ISIS and its capabilities have been weakened and the strategy is unchanged.

Obama understands that an element of his legacy will be the hand-off to the next president of the U.S.- and Iraqi-led operation to defeat ISIS, also known as ISIL, his spokesman said, noting how firmly Obama believes Iraqis must fight for their own country.

“The president has indicated that … essentially, this is a 36-month military operation that will be in the degrade phase,” White House Press Secretary Josh Earnest said. “He has been candid about the fact that this will be a challenge that the next president will have to confront.”

Obama authorized U.S. air strikes against ISIS last summer, and has sent U.S. special operations forces, military and intelligence advisers, trainers and weapons -- including 1,000 antitank rockets -- to Iraq at the request of the new government, led by Prime Minister Haider al-Abadi, who was elected last year.

The president will not consider sending U.S. combat troops to fight ISIS, Earnest repeated Thursday, describing Obama’s belief that helping the Iraqis try to degrade ISIS is the best long-term strategy, rather than a “full-scale reinvasion” of Iraq.

His comments were intended to draw a comparison to President Bush’s decision to wage war in Iraq to topple Saddam Hussein and seize weapons of mass destruction. The Bush administration later conceded WMD had not existed as a threat that could fall into al Qaeda hands, and President Bush subsequently called it an intelligence “mistake.”

At the State Department Thursday, Deputy Spokesperson Marie Harf denied that Obama’s meeting Tuesday with his national security team triggered a formal re-evaluation of the U.S. and coalition efforts to degrade ISIS. But her references to “taking stock” of strategy and tactics undercut the administration’s no-changes-ahead assurances.

“There's no formal strategy review,” she said. “This is an ongoing process we always have of taking stock of what's happening on the battlefield in a variety of places, and how best, strategically and tactically, to approach the situation.”

The White House, citing Defense Department metrics, believes ISIS no longer operates freely in 25 to 30 percent of the populated territory it once held and from which it could hunker down to plot attacks aimed at the United States. That point – safety and security of Americans, rather than the defense of Iraqis – is at the heart of Obama’s definition of national security where ISIS is concerned.

“We are in the degrade phase of this effort and we are making progress in degrading the capability of ISIL,” Earnest said, conceding that ISIS fighters’ destruction and mass slaughter in Ramadi amounted to “a setback.”

Asked what might trigger Obama to alter a prolonged strategy he is defending in the face of significant setbacks, Earnest pointed to the Iraqis, their capabilities, and conditions on the ground where ISIS is battling for control.

“This strategy is one that is constantly being refined,” the president’s spokesman said. “It's part of a judicious application of experience and data … [which] we're receiving on the ground and information that we're receiving from our partners in Iraq.”

The White House challenged its critics, arguing that none has proposed feasible alternatives to tactics and tools beyond those the United States and coalition partners have committed.

“We hear them complain about the pace of progress,” Earnest said. “There's no doubt the president would like to see more progress, too, but he understands that the kind of strategy that we're currently pursuing is entirely consistent with our national security interests.”

U.S. taxpayers are spending an average of $8.6 million a day on the operation to degrade ISIS in Iraq and Syria, according to the Pentagon.