A Terminal High Altitude Area Defense (THAAD) interceptor is launched during an intercept test in this undated photo. (U.S. Defense Department Missile Defense Agency via Reuters)

Plans to deploy an American antimissile battery to South Korea and the growing North Korean threat will be at the top of James Mattis’s agenda this week when the new defense secretary visits South Korea and Japan on his first foreign trip.

Mattis, a retired Marine general nicknamed “Mad Dog,” will meet with Han Min-koo, the South ­Korean defense minister, in Seoul on Thursday before heading to Tokyo. Han is expected to reiterate South Korea’s commitment to hosting the Terminal High Altitude Aerial Defense system, or THAAD.

But with China exacting economic revenge on South Korea over its decision to host the missile battery and the South Korean government in crisis, some in Seoul now have jitters about the plan.

Moon Jae-in, an opposition candidate running at the top of the presidential polls, has said decisions on the THAAD deployment should wait until the next South Korean administration is in place.

That could take months, with the Constitutional Court now deciding whether to uphold the National Assembly’s motion to impeach President Park Geun-hye, who made the decision to host THAAD, for her role in a sensational political scandal. If the court forces her from office, elections must be held within 60 days. Otherwise, they will take place in December as scheduled.

Defense Secretary James Mattis, left, stands with Jordan's King Abdullah II bin Al-Hussein during an honor cordon at the Pentagon on Monday. (Andrew Harnik/AP)

In the meantime, the Chinese government — which has made no secret of its opposition to the THAAD plan — is trying to persuade South Korean political leaders to change their minds.

Although Washington and Seoul insist that its purpose is to guard against the threat of North Korean missiles, Beijing views the system as another attempt to curtail its military expansion.

In recent weeks, China has slapped a number of trade sanctions on South Korea in an apparent effort to dissuade Seoul from going ahead with the deployment.

“China is one of the biggest reasons why people are opposing THAAD, and I would say that it’s based on reasonable concerns,” said Kim Dong-yub of the Institute for Far Eastern Studies in Seoul. “Just go into a department store and you can feel the change,” he said, referring to the sudden drop in Chinese tourists coming to South Korea.

In the past month, China has banned imports of South Korean bidet toilet seats and South Korean cosmetics, which are hugely popular among young women who love Korean dramas. Classical musicians have joined “K-pop” stars in having visas denied and concerts canceled.

(Jason Aldag/The Washington Post)

Meanwhile, department stores in China run by Lotte, the South Korean retail group, have been subject to a sudden flurry of safety and hygiene inspections and tax audits, although Beijing rejects any suggestion that this is related to THAAD.

Lotte owns the country club 200 miles from Seoul earmarked for the THAAD battery. It will swap with the government for another parcel of land.

Lotte appeared to be taking it slow with the internal procedures needed to be completed before the swap can take place, a possible sign that it is worried about the impact on its business in China. It has more than 150 stores in China and is building a huge retail and amusement park complex in the southwestern city of Chengdu.

Chinese tourists accounted for more than 70 percent of Lotte Duty Free’s sales in the first quarter of last year. “It is true that we are sandwiched between our role as a South Korean enterprise, South Korea’s relations with China and possible economic loss,” the Yonhap News Agency quoted a senior Lotte official as saying.

Small South Korean companies are suffering, too. There has been a sharp decrease in Chinese tourists, said Kim Seo-kyung, who owns a clothing store in Myeongdong, a fashion district in Seoul usually teeming with Chinese shoppers.

“Maybe it’s because of THAAD and because the relationship between South Korea and China has soured,” Kim said. She estimated that her revenue had fallen about 40 percent since last year.

Businesses around South Korea reported a sharp drop in tourist numbers over the Lunar New Year holiday this past weekend.

American proponents of THAAD say they hope South Korean authorities will not waver.

“The THAAD is a far more effective ballistic missile defense system than anything South Korea has or will have for decades,” said Bruce Klingner, a Northeast Asia specialist at the Heritage Foundation. “To not deploy THAAD is to choose to put South Korea and U.S. forces stationed there at grave risk to North Korean nuclear, chemical and biological attack.”