Jack Beyrer of the Washington Free Beacon reports bad news about two American rivals.

Russia is joining China in a series of military exercises in August, a sign of growing coordination between the two countries that experts say threatens American security.

The Chinese propaganda newspaper Global Times reported that Moscow will dispatch Russian forces—including aircraft and artillery—to the Chinese province of Ningxia. The Times specifically sets the exercises in the context of “mutual trust” between the two militaries, which they say form a “backbone” against the United States in the region. This exercise is the first in which Russian troops trained on Chinese land, as opposed to earlier exercises in the Russian Far East or maritime demonstrations.

According to retired Air Force general Dave Stilwell, a former State Department official, the exercises warrant a closer study of China’s interest in working with the regime of Russian president Vladimir Putin.

“It’s worth assessing why China is suddenly more serious about increasing cooperation with Russia,” Stilwell told the Washington Free Beacon. “The more Beijing can get Moscow to soak up U.S. attention and U.S. forces, the less Beijing will have to deal with in the Pacific.”

The exercise is only the latest instance of Russian and Chinese cooperation on military projects. The two American adversaries have repeatedly worked together to field advanced weapons systems, such as submarines and missile warning systems, while also inking an agreement to work together to counter American interests in space. And Russian defense technology has empowered the Chinese Navy.

Richard Weitz, the director of the Hudson Institute’s Center for Political-Military Analysis, said cooperation between Moscow and Beijing poses a major problem for U.S. defense planners. American resources could be stretched thin as the United States attempts to confront two rising hostile powers.

“Even if it’s not a formal military alliance, it causes a lot of problems for us—particularly in military technology—and that could increase,” Weitz said.