Trump is demanding that South Korea pay roughly 400% more in 2020 to cover the cost of keeping US troops on the peninsula, a congressional aide and an administration official confirmed to CNN.

The price hike has frustrated Pentagon officials and deeply concerned Republican and Democratic lawmakers, according to military officials and congressional aides. It has angered and unnerved Seoul, where leaders are questioning US commitment to their alliance and wondering whether Trump will pull US forces if they don’t pay up.

“Nothing says I love you like a shakedown,” said Vipin Narang, an associate professor at MIT who follows the Korean peninsula, summarizing South Korean uncertainty about the US.