The Trump administration recently pulled out 1,000 U.S. troops helping to fight ISIS in northern Syria, leaving our Kurdish partners and allowing Turkey to invade. Many lawmakers, including those in the president's own party, have condemned President Trump's decision to do so.

But a recent CBS News poll found that 41% of respondents hadn't heard enough about the situation to approve or disapprove of the decision.

On this week's episode of the "Where Did You Get This Number?" podcast with Anthony Salvanto, Anthony sits down with CBS News national security correspondent David Martin to discuss the context concerning why U.S. troops were in Syria, and more broadly, how the U.S. military assesses threats around the world.

The northern border region of Syria is important to the U.S. because it was the base for the campaign against ISIS, which Martin characterized as defeated but not destroyed. Once Turkey entered the region to fight our Kurdish allies, the campaign against ISIS would collapse.

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"There was no need for American troops any longer in Syria, hence the withdrawal order," Martin said.

The presence of U.S. troops in a region can sometimes be a deterrent to prevent military action, but Martin highlights the irony that Turkey still sent troops into the northern Syrian region despite the 1,000 American troops there.

"Turkey knew that the U.S. wasn't going to fight. They could just basically roll on over us," Martin said, in contrast with U.S. troops in Europe. Martin said we were caught between two allies, "one of which we can afford to throw overboard, namely the Kurds, and one of which we can't afford to throw overboard, namely the Turks."

In terms of threats and priorities, Martin said the top priority for each of the past 3 Secretaries of Defense has been China, which requires a military presence in the Pacific.

"But if you have to send 2,000 troops to Syria, 14,000 troops to Afghanistan, 5,000 troops to Iraq, and on and on, it gets harder and harder to sustain a military presence in the Pacific," Martin said. "So the Pentagon is all for getting out of these wars as quickly as possible. They just don't want to pull out and then have a resurgence of the terrorists."

Martin cited the Obama administration's 2011 decision to pull U.S. combat troops out of Iraq, against the advice of military and intelligence officers, which is now regarded as contributing to the rise of ISIS.

Subscribe to "Where Did You Get This Number?" and download the latest episode to learn more about the fight against ISIS, the track record of ceasefires in Syria, global threats to the U.S., what it's like covering the Pentagon, and more.

The podcast is available on Apple Podcasts, Google Play, Stitcher, Spotify, or wherever you get your podcasts.

Host: Anthony Salvanto, Director of Elections and Surveys at CBS News

Guest: CBS News Pentagon Correspondent David Martin

Intern: Maeve Burke

Producer: Allen Peng

Twitter: @WDYGTN

Instagram: @getthisnumber