Davis Love III's men are 8-4 in front following the second session of foursomes on day two at Medinah, as Europe have struggled to make birdies.
Langer, who is in Chicago for the tournament, believes that Europe can still win if they stay within five points by tomorrow's singles.
"Europe have got a very tough battle on our hands," he told BBC Sport. "The USA have home advantage and some very good putters on their team, but there are still 12 points available tomorrow, and anything can happen.
"Most of the Americans are in form and some of our guys are not. We have some good ball-strikers but sometimes the putting isn't always their strengths. These greens are lightning fast and sloping, but you've got to make the putts to win the Cup.
"If Europe are only two or one behind overnight then that would be awesome. Four or five behind and it will be very tough tomorrow."
Langer was a victorious captain at Oakland Hills in 2004.