President Barack Obama's decision to send still more American troops to Iraq, and to put military advisers closer to the front lines against the Islamic State, fits a pattern of ever-deepening involvement in a country whose war Obama exited with supposed finality in December 2011.

From the initial contingent of 170 U.S. soldiers who entered Baghdad as advisers in June 2014, after the Islamic State overran much of northern and western Iraq and seemed poised to threaten Baghdad, the troop total jumped to 1,550 six months later. It topped 3,000 in April 2015 and then edged higher. The latest increase announced Monday by Defense Secretary Ash Carter pushes the authorized total above 4,000. More increases seem likely.

What the Pentagon calls "tightening the noose" on the militants, critics call indecisive steps with limited chance to succeed.

One of the most vocal critics of Obama's Iraq policy, Republican Sen. John McCain, dismissed Carter's announcement that the U.S. would send another 217 troops to Iraq in support of the Iraqi security forces' preparation for an assault on the Islamic State stronghold of Mosul.

"Grudging incrementalism," McCain called it.

Patrick Martin, an Iraq specialist at the Institute for the Study of War, is skeptical that the U.S. approach is sufficiently aggressive.

"The addition of 217 advisers ... is not going to be nearly enough to actually make a significant difference on the ground in the near future," he said in an interview. On the other hand, the U.S. offer to fly Apache attack helicopters in support of an Iraqi advance toward Mosul is a significant move, Martin said, noting that it would be the first time the Iraqis have accepted that kind of support since U.S. forces returned to Iraq in 2014.

Obama's approach in Iraq has been tempered not just by his pledge to end U.S. military involvement there after he took office in 2009 but also by the Iraqis' own political failings, which even now cast doubt on the durability of any battlefield victories U.S. troops can help the Iraqis achieve. In 2007, at the peak of the Iraq war, the U.S. had about 170,000 troops there.

Rather than commit large ground combat units to Iraq or Syria, Obama in 2014 opted for providing a support role on the ground, backed by bombing from the air. Obama was on his way Tuesday to Saudi Arabia to encourage Gulf Arab countries to contribute more to the battle in Iraq.

Nearly two years later, the Islamic State has been weakened and squeezed but remains a credible threat. It not only holds territory in Iraq and Syria but also has spread to Libya and Afghanistan while launching deadly attacks in Paris and Brussels.

On a visit to Baghdad this week, Carter described the decision to deploy another 217 soldiers as "more of the same," in the sense that it aligns with the U.S. strategy of providing more support to Iraqi forces as they gain momentum, while not doing the fighting for them.

"Our strategic approach makes sure that the defeat of ISIL is lasting," he said, using a common acronym for the Islamic State. "It is to enable capable and motivated local forces to sustain the defeat. We are committed, I am committed, to doing more to accelerate that defeat. We want to do it as fast as we possibly can."

It has taken this long to bring Mosul within the Iraqis' gunsights because they have been slow to leverage U.S. training, partly because of sectarian conflict and political gridlock in Baghdad. Four months ago the Iraqis recovered Ramadi after collapsing there in May 2015, which prompted Carter to question their will to fight. They still lack essential ingredients for battlefield success such as close-air support for maneuvering ground forces, and it's not clear they will retake Mosul before 2017, even with additional American support.

Most of the additional 217 troops would be Army special forces, who have been used throughout the anti-Islamic State campaign to advise and assist the Iraqis. For the first time, the advisers are authorized to assist the Iraqis at battalion level, meaning with smaller Iraq combat units likely to be closer to the front lines.

The extra U.S. troops also would include trainers, soldiers to provide security for the advisers, as well as maintenance teams and crews for the Apache attack helicopters that Carter said the Iraqi government has agreed would be needed to provide close-air support for ground forces in a Mosul assault. The U.S. also will provide additional sets of mobile artillery, known as HIMARS, to support Iraqi ground forces as they advance toward Mosul.

And those are unlikely to be the last additions to the U.S. military presence. Lt. Gen. Sean MacFarland, the top U.S. commander in Iraq, told reporters Monday that the focus for now is on getting the Iraqis to fully isolate Mosul and set the right conditions for recapturing it.

"The next step of that obviously is to actually clear the city," MacFarland said. "And when we get to that step, that will be another conversation that we'll have" about U.S. support. For now, he said, "We're going to employ these additional authorities and capabilities and see how far it takes us. And then if it doesn't take us all the way, we'll come back and have another discussion and ask for more if we need to."

Asked whether this was incrementalism, MacFarland said, "I would prefer to call it a step-by-step approach. We're on the first step right now."

Associated Press reporter Lolita C. Baldor contributed to this story from Baghdad.