President Donald Trump announced an open-ended commitment to Afghanistan that will put as many as 4,000 more U.S. troops into the nation’s longest-lasting conflict and keep American forces there as long as it takes to deny terrorists a haven and bring about a political settlement with the Taliban.

The decision marks a turnabout for Trump, who during the campaign only grudgingly acknowledged the need for the U.S. presence in Afghanistan and promised to eschew military entanglements and nation-building abroad to focus resources at home.

“Our nation must seek an honorable and enduring outcome worthy of the tremendous sacrifices that have been made,” Trump said Monday in a nationally televised address from the Fort Myer Army base in Virginia. “The consequences of a rapid exit are both predictable and unacceptable.”

Trump is now the third U.S. president to struggle with how to get out of Afghanistan, a country beset by ethnic, religious, cultural and tribal factions amplified by foreign powers including the U.S. as well as neighboring Pakistan and Russia. That mixture has stymied foreign armies for centuries.

Trump declined to specify the number of troops the U.S. would have in Afghanistan or detail what criteria would be used to determine success. But his strategy gives the green light to a plan by Defense Secretary James Mattis to bolster training and support for the Afghan army with roughly 4,000 additional personnel — a 50 percent increase in the current American military presence. Mattis said in a statement Monday night that several U.S. allies also have committed to increasing troop numbers.

Just as Trump has said China is the key to another longstanding U.S. foreign policy dilemma — persuading North Korea to dismantle its nuclear programs — the president’s approach focuses on making Pakistan a central component of his strategy.

“We can no longer be silent about Pakistan’s safe havens for terrorist organizations, the Taliban, and other groups that pose a threat to the region and beyond,” Trump said. “Pakistan has much to gain from partnering with our effort in Afghanistan. It has much to lose by continuing to harbor terrorists.”

Rather than a bold break with previous U.S. strategy in Afghanistan, Trump is making an adjustment that emphasizes diplomatic and economic pressure as much as military might. But the approach fits a pattern that’s emerged in Trump’s foreign policy agenda, which avoids the Obama administration penchant for setting firm deadlines or milestones to get what the U.S. wants.

“A core pillar of our new strategy is a shift from a time-based approach to one based on conditions,” Trump said. “I’ve said many times how counterproductive it is for the United States to announce in advance the dates we intend to begin, or end, military operations.”

He said the U.S. commitment “is not unlimited, and our support is not a blank check.” Although he talked of using economic development as leverage, Trump insisted, “We are not nation building again. We are killing terrorists.”

He called his approach “principled realism.”

How the new strategy is received by the public and lawmakers may determine whether Trump can put behind him the multiple controversies and missteps of the past week, one of his most tumultuous in office.

Increasingly Isolated

He’s become increasingly isolated from the Republican establishment in Washington and corporate leaders after his response to Aug. 12 violence in Virginia appeared to confer legitimacy on white supremacists. At the same time, the abrupt departure of chief strategist Stephen Bannon on Friday risks distancing the president from the core of his political support.

Several senior Republicans quickly praised Trump’s address. John Cornyn, the No. 2 Senate Republican, called it a “welcome speech,” and Republican Senator Marco Rubio of Florida tweeted, “Good #AfghanStrategy & excellent speech by @POTUS laying it out to the nation.”

House Speaker Paul Ryan, a Wisconsin Republican, said during a CNN town hall event that he was pleased with what he called “a new Trump doctrine” in Afghanistan.

Trump had been a harsh critic of the U.S. intervention, tweeting in 2013, “We should leave Afghanistan immediately. No more wasted lives.” But during his run for the presidency, he shifted, saying in a CNN interview that he “would leave the troops there begrudgingly. Believe me, I’m not happy about it.”

On Monday night, Trump acknowledged his view had evolved.

“My original instinct was to pull out, and historically I like following my instincts, but all of my life I heard that decisions are much different when you sit behind the desk in the Oval Office,” he told his audience at the base, which is adjacent to Arlington National Cemetery just outside the nation’s capital.

Vice President Mike Pence disagreed with critics’ assessments that Trump’s announcement constituted a “flip-flop.” “The last administration engaged in a short-term surge and then announced a timeline for withdrawal, emboldening the enemy,” Pence said in an interview with NBC on Tuesday. Trump provided a whole new strategy of “resolve and commitment” that involves not only Afghanistan, but other countries in the region, he said.

As troop levels have waxed and waned since then — President George W. Bush sent special forces to help oust the Taliban government for harboring Osama bin Laden after the Sept. 11, 2001 terror attacks — the U.S. position has deteriorated.

‘Not Winning’

While Mattis told lawmakers in June that the U.S. is “not winning in Afghanistan right now” — despite spending about $714 billion since 2001 — the latest report by the U.S. special inspector general for Afghanistan reconstruction shows how bad the situation has become.

American and NATO Military personnel are hunkered down behind blast walls while attacks by Taliban and al-Qaeda militants spike, according to the report. The government of President Mohammad Ashraf Ghani controls only about 60 percent of the country.

South Asia

The path forward under the new strategy extends beyond Afghanistan’s borders. Planning for the new strategy, including at a Camp David meeting at the end of last week, includes the U.S. approach to South Asia. That reflects the view of Mattis and Secretary of State Rex Tillerson that any solution for Afghanistan requires getting tough on neighboring Pakistan for sheltering the Taliban and other groups.

The president agreed in June to let Mattis send more personnel to reinforce the approximately 8,500 U.S. forces in Afghanistan. But the defense secretary held off deploying the additional troops until a broader strategy was in place. Now Trump will have to lean on alliances he’s sometimes denigrated to accomplish his goals and engage in the sort of nation-building that he campaigned against.

Trump said he will give more authority to military commanders and lift restrictions that he said were hindering the ability of troops in the field to target terrorist and criminal networks throughout Afghanistan.

“But we will no longer use American military might to construct democracies in far away lands, or try to rebuild other countries in our own image,” he said, “those days are now over.”