David Jackson

USA TODAY

President Obama doubled down Wednesday on an increasingly questioned pledge: There will be no U.S. ground combat troops back in Iraq.

"I will not commit you, and the rest of our armed forces, to fighting another ground war in Iraq," Obama told troops at the U.S. Central Command in Tampa, Fla.

After a briefing with military leaders at CENTCOM, Obama said forces in Iraq and Syria must fight ground battles against the Islamic State, a jihadist group also known as ISIL and ISIS.

Obama also said the United States — which is conducting airstrikes in Iraq and planning them in Syria — will be joined by a coalition of other nations under threat by the Islamic State.

"This is not and will not be America's fight alone," Obama said.

The renewed pledge of no U.S. combat troops came amid some skepticism over whether the United States can follow through on a plan that relies on Iraqi and Syrian forces to roll back the Islamic State.

Robert Gates, former Defense secretary for Obama and predecessor George W. Bush, has questioned whether the president can achieve his goal of defeating the Islamic State without U.S. ground forces.

"They're not gonna be able to be successful against ISIS strictly from the air, or strictly depending on the Iraqi forces, or the Peshmerga, or the Sunni tribes acting on their own," Gates told CBS This Morning. "So there will be boots on the ground if there's to be any hope of success in the strategy."

Gates also told CBS that Obama is doing himself a disservice by echoing his pledge against combat troops.

"I think that by continuing to repeat that, the president in effect traps himself," Gates said.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, said in congressional testimony Tuesday: "To be clear, if we reach the point where I believe our advisers should accompany Iraqi troops on attacks against specific ISIL targets, I will recommend that to the president."

Dempsey and administration officials stressed that Dempsey supports the plan as-is and was answering hypothetical questions from lawmakers. His comments referred to U.S. advisers who will work with Iraqi forces, not U.S. ground combat units.

Tamping down questions about a mission expansion, White House spokesman Josh Earnest said Obama would not even "review or consider" options that include U.S. combat troops.

Obama campaigned for the White House — twice — on pledges to wind down and end wars in Iraq and Afghanistan.

The administration's plan against the Islamic State, unveiled last week, relies on training Iraqi and Syrian forces to take the ground fight to the Islamic State. The United States is focusing on airstrikes against IS positions, starting last month in August and perhaps extending to Syria later.

"After a decade of massive ground deployments, it is more effective to use our unique capabilities in support of partners on the ground so they can secure their own countries' futures," Obama told the troops in Tampa. "We'll use our air power ... We will train and equip our partners."

He also said: "The American forces that have been deployed to Iraq do not and will not have a combat mission. They will support Iraqi forces on the ground as they fight for their own country against these terrorists."

Some lawmakers, particularly Republicans, have questioned whether the plan will be enough, especially without more troops.

"We have made this decision not to have ground troops," said Rep. Jack Kingston, R-Ga. "We do not need another half-pregnant war in the Middle East. If it is important enough to fight, it's important enough to win."

Iraq's new prime minister, Haider al-Abadi, backed Obama's no-combat position, telling the Associated Press that foreign ground troops are not necessary or wanted in the fight against the Islamic State.

While the Islamic State does not pose an immediate threat to the United States, Obama told the troops at Central Command that "its leaders have repeatedly threatened America and its allies."

The president has deployed some 1,600 advisers to Iraq in advisory and assistance roles, including defense of the U.S. embassy in Baghdad and the U.S. consulate in Irbil.

Moving forward, the anti-Islamic State plan could involve the covert use of special forces, but that is not something Obama and aides will discuss in public.