Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is the author of the forthcoming book " United States of Jihad: Investigating America's Homegrown Terrorists ."

Like many of Trump's charges this one doesn't hold much water. Clinton left the State Department in January 2013 and ISIS wasn't even founded until three months later.

But Trump's charge does raise an interesting question, which is how best to assign responsibility for the rise of ISIS, including the issue of how might the Obama administration's exit from Iraq at the end of 2011 have helped smooth the path for ISIS?

It began with a thug

The rise of ISIS starts with a Jordanian thug named Abu Musab al-Zarqawi who founded ISIS' parent organization, al Qaeda in Iraq.

It was Zarqawi who inaugurated al Qaeda in Iraq's televised beheadings with the killing of American businessman Nick Berg in 2004. And it was Zarqawi who ignited a civil war against the Shiites in Iraq the same year. These tactics and policies remain today at the core of ISIS.

What gave Zarqawi the opportunity to create al Qaeda in Iraq? It was, of course, George W. Bush's decision to invade Iraq in 2003. Iraqi dictator Saddam Hussein brutally repressed all forms of opposition to his regime and before the Iraq War al Qaeda had no presence in Iraq.

Al Qaeda in Iraq grew in strength in 2006 so that it controlled much of the massive Anbar province in western Iraq. At the beginning of 2007, Bush authorized a surge of new troops and brought in a new commander, David Petraeus. Allied with a movement of Sunni tribesmen angered by al Qaeda known as "the Awakening," U.S. troops had largely extirpated al Qaeda from Iraq by 2008.

The 4 big factors

So how did al Qaeda in Iraq surge back as ISIS?

There are four big factors. The first is the Syrian civil war, which launched in 2011 in reaction to President Bashar al-Assad's brutal repression of peaceful protests against his dictatorship. Elements of what would become ISIS traveled from Iraq into Syria to fight against Assad. Those forces gained strength in Syria, which they drew upon when they re-entered Iraq as a reinvigorated force in 2013, seizing much of Anbar a year later as well as Mosul, the second-largest city in Iraq.

The second factor was the role that some of Hussein's former officer corps played in helping ISIS to its victories. A number of the late dictator's former commanders helped to professionalize ISIS as a fighting force. (The Bush administration's decision to disband the Iraqi army in 2003 had helped push some Iraqi officers to join Sunni militant groups.)

The third factor was the feckless and incompetent rule of then-Iraqi Prime Minister Nuri al-Maliki, who marginalized Sunnis and disenfranchised them from Iraq's political process to the point that many Sunnis preferred the rule of the Islamist militants in ISIS to that of the "Shia" government in Baghdad. Inexplicably, the Obama White House kept backing Maliki despite his manifest flaws as a leader.

The fourth factor was the hollowing out of the Iraqi army , which simply ran away as ISIS made its most dramatic advances during the first half of 2014. The Iraqi army was poorly led, poorly paid and riven with corruption.

None of these factors can be easily ascribed to Obama or to Clinton, although certainly they did preside over the withdrawal of all U.S. troops from Iraq at the end of 2011, a plan bequeathed to them by Bush.

'JV' team?

Could the Obama administration have fought harder to retain a U.S. troop presence in Iraq? Possibly.

Would the Iraqi government have allowed such a presence? Not likely as the Iraq government was by the time of the U.S. withdrawal more aligned with Iran than with the United States.

Obama was also slow to recognize the threat posed by ISIS, famously referring to the Islamist terrorist group gaining ground in Syria and Iraq as a "JV" team in a January 2014 interview.

Since the summer of 2014 the Obama administration has mounted -- at least from the air -- an aggressive campaign against ISIS, but it has proven reluctant to do much on the ground.



Could more be done? Yes. More U.S. Special Forces fighting side by side with Iraqi forces and more U.S. forward air controllers calling in close air support would certainly help the Iraqi military against ISIS.

In Syria, a no-fly zone targeted at Assad's air force and safe zones for refugees fleeing the fighting would help tamp down the death toll that plays into the hands of ISIS and other Sunni militants who can position themselves as the only groups that are really defending the Sunni population.

Rather than making loose and unsubstantiated claims that Obama and Clinton created ISIS, it would behoove Trump if he advanced some real policy ideas about how to solve the Syrian and Iraqi civil wars. Of course, to do that he would have to get beyond the inflammatory slogans and sound bites that have characterized his campaign.