The U.S. military continues to make progress fielding a Terminal High Altitude Area Defense System (THAAD) battery in South Korea but might not declare it operational until after that country’s May 9 presidential election, according to a White House foreign policy adviser.

“It should be a decision for the next president,” the adviser told reporters April 16, according to a transcript released by the White House. The adviser’s comments came during Vice President Mike Pence’s visit to the region.

The two leading presidential candidates are reportedly split on THAAD, with Ahn Cheol-soo supporting the deployment and Moon Jae-in pledging to review the issue amid Chinese opposition to the system. The winner will replace President Park Geun-hye, who was removed from office due to a corruption scandal.

In July, the United States and South Korea agreed to the THAAD fielding in response to North Korea’s missile and nuclear weapons development. Elements of the Lockheed Martin [LMT] system, including truck-mounted interceptor launchers, began arriving in South Korea in early March. U.S. Forces Korea officials have indicated that the system would become operational by May.

THAAD is designed to destroy short- and medium-range ballistic missiles inside or outside the Earth’s atmosphere in their final phase of flight.