It was a “serious mistake” for President Obama to draw a “red line” in 2012 on Syria’s use of chemical weapons, former Secretary of Defense Robert Gates said Wednesday. 

Speaking to The Wall Street Journal, Gates said: “I always used to say to presidents, ‘if you cock the pistol, you gotta be willing to fire it.' "

Laying out his philosophy on war, the former Defense chief said the United States should be “extremely careful about preventive war.” Gates said war depends on accurate intelligence, and the United States should not be overly confident it “can get it right.”

During a press conference in 2012, the president said Syrian President Bashar Assad’s regime would cross a “red line” if the administration started seeing “a whole bunch” of chemical weapons being used in the country. 

A limited military strike in the country seemed imminent last year after the administration concluded that the Assad regime had killed more than 1,000 people with chemical weapons. 

However, a diplomatic agreement was eventually reached as Syria agreed to destroy its chemical weapons stockpile by mid-2014. 

The U.S. ship set to help destroy the weapons is set to depart later this week or early next week after the first deadline at the end of December was missed. 

Gates has been making the media rounds as he promotes his new book Duty: Memoirs of a Secretary at War. While generally positive, Gates criticizes the administration on a number of points in the book. 

The former Defense secretary has been critical of Obama’s “red-line” comment before.

Speaking at a forum in Dallas last September, he disagreed that the enforcement of Obama’s “red line” was justification for an attack. 

"I believe to blow a bunch of stuff up over a couple of days to underscore or validate a point or principle is not a strategy," Gates said at the time.