SIMI VALLEY, Calif. — Republican presidential candidate Jeb Bush said Tuesday the U.S. may need to send more ground troops into Iraq to defeat Islamic State militants, but he stopped short of saying how many as he outlined his strategy for combating a threat that’s “spreading like a pandemic.”

In the first major foreign policy speech of his White House bid, Bush sharply criticized Hillary Rodham Clinton’s tenure as secretary of state and accused the Democratic front-runner and President Barack Obama of allowing the militant group to take hold in the Middle East.

“Who can seriously argue that America and our friends are safer today than in 2009, when the president and Secretary Clinton — the storied ‘team of rivals’ — took office?” Bush said. “So eager to be the history-makers, they failed to be the peacemakers.”

Along with saying he would potentially boost the number of U.S. troops in Iraq, where roughly 3,500 American military trainers and advisers are already helping Iraqi forces fight the Islamic State group, Bush offered a broad look at how he would take on the group in neighboring Syria — which Bush and Middle East experts agree is a far more complicated task.

Beating back the Islamic State there will require the removal of that country’s president, Bashar Assad, Bush said. To do so, he said he would aim to unite the moderate forces in that country and for U.S. troops to “back them up as one force.”

“And we should back that force up all the way through — not just in taking the fight to the enemy, but in helping them to form a stable, moderate government,” he said. “It’s a tough, complicated diplomatic and military proposition, even more so than the current situation in Iraq. But it can be done.”

Bush has previously touched on aspects of his strategy for Iraq, such as allowing the training and advisory troops already in the country to join Iraqi forces on the battlefield and help in better guiding airstrikes. He again expressed support for a no-fly zone in Syria.

In his speech at the Ronald Reagan Presidential Library, Bush tied the rise of the Islamic State, a militant Sunni group that occupies a large swath of Iraq and Syria and has a presence elsewhere, to the departure of U.S. forces from Iraq in 2011.

“ISIS grew while the United States disengaged from the Middle East and ignored the threat,” he said. “And where was Secretary of State Clinton in all of this?” Answering his own question, he said Clinton “stood by as that hard-won victory by American and allied forces was thrown away.”