America's longest war is approaching its 17th year.

As part of our series, Issues That Matter, we took a closer look at the conflict in Afghanistan with Michèle Flournoy, who served as undersecretary of defense for policy under President Obama from 2009 to 2012.

"The real issue here is a political strategy," Flournoy told "CBS This Morning" Tuesday. Flournoy is also the co-founder and CEO of the Center for a New American Security.

The war in Afghanistan was launched on October 7, 2001 in response to the September 11 attacks.

"I think first of all, the Taliban has proven to be a very resilient insurgency. They have support from Pakistan, they have support from outside countries. We've had an Afghan government that's been very weak and really plagued by corruption. And we, too, have made mistakes," Flournoy said.

Flournoy pointed to the years from 2003 to 2009 when she says the U.S. focus was largely switched to Iraq.

"When President Obama came in and launched the surge [of U.S. troops in Afghanistan] in 2009, that was important to regaining momentum, but he also announced that that surge would only last a short while -- about less than two years -- and so the Taliban had the signal, you know, we can just wait this out," Flournoy said.

Defense Secretary James Mattis told a Senate committee last month the United States is not winning the war. Flournoy doesn't disagree.

"It's really a stalemate at this point. The good news is that the Afghan forces are in the lead and with our support they continue to hold their own, but they do need our continued support," Flournoy said.

"The real issue here is a political strategy. How do we use that leverage of additional troops supporting the Afghans to actually get the Taliban to the negotiating table. Nobody's gonna win this on the battlefield."

Asked how much territory the Taliban controls now compared to 9/11, Flournoy said, "It controls more now than when we first started the war."

"We have evidence that Russia's proving small arms to the Taliban. Also Iran. So we have this problem of outside support," Flournoy said.

She said the countries providing support are "hedging their bets" in case the Taliban wins, but it also provides them a chance to "poke the United States."

The Trump administration is reviewing U.S. policy on Afghanistan and in comments last week, the president said, "I want to find out why we've been there for 17 years."

What does Flournoy think officials should consider? "What I think we want to see coming out of the Trump administration is a very clear statement of commitment. Look, we have to remember, why are we there? We are there because we don't want Afghanistan to once again become a safe haven for terrorists that could strike the United States," Flournoy said. "The last thing we want is for ISIS to pick up and move from Syria to Afghanistan because we're not pushing back hard enough."

Asked what Trump should do, Flournoy said, "I think the most important thing beyond the troop numbers is a political strategy -- you have to have a broader strategy into which the military portion fits. You have to have a way to get the Taliban to the table."

"The U.S. has to signal a long-term commitment to Afghanistan as a partner for fighting terrorism in the region. If there's any waffling, any sense that we're not fully committed the Taliban will continue to wait us out," Flournoy said.