President Trump’s trade war, a planned U.S. arms sale to Taiwan, and routine ship movements have all combined to sour relations between the U.S. and Chinese militaries, but Defense Secretary Jim Mattis says this too will pass.

“I don’t think that we are seeing a fundamental shift in anything,” Mattis told reporters outside the Pentagon Tuesday. “We’re just going through one of those periodic points where we’ve got to learn to manage our differences.”

China, which has called the sale of $330 million in U.S. military equipment and spare parts to Taiwan “a violation of international law,” has denied permission for a U.S. warship to make a routine port visit in Hong Kong next month and demanded the arms sale be canceled.

Under the 1979 Taiwan Relations Act, the U.S. does not support independence for Taiwan but does commit to assist Taiwan in maintaining its defensive capabilities.

The war of words between the U.S. and China escalated Wednesday, when Trump accused the Chinese government of unspecified meddling in the November midterm elections in an attempt to wound the president politically.

“They do not want me or us to win, because I am the first president ever to challenge China on trade, and we are winning on trade, we are winning at every level,” Trump said while chairing a session of the U.N. Security Council. “We don't want them to meddle or interfere in our upcoming election.”

[Related: Trump accuses China of 2018 election interference 'against my administration']

China continues to complain about what the Pentagon calls “freedom of navigation” operations in the South China Sea, in which both planes and ships make a point of asserting the right to transit though international air and sea lanes.

In July, the U.S. sent the destroyers USS Mustin and USS Benfold through the narrow Taiwan Strait in what the U.S. Pacific Fleet called “a routine transit.”

“There’s nothing out of the ordinary about it, nor about our ships sailing though there,” Mattis said. “It’s international waters, folks.”

Mattis said he’s unconcerned about the current spike in tensions, adding the military-to-military relationship between Washington and Beijing remains intact.

“The level of participation and collaboration may go up and down at times, but there’s a strategic relationship I think both sides recognize the need for,” he said.

As for Beijing denying the amphibious assault ship USS Wasp permission to make a port call in Hong Kong, “I’m not sure what to make of it right now,” Mattis said. “We’re sorting out, obviously, a period with some tension there, trade tension, and all so we’ll get to the bottom of it.

But Mattis also blamed much of the tension on China’s expansionist claims to a large swath of the South China Sea, including fortifying man-made islands with airstrips and military hardware.

That is why, Mattis says, routine flights of U.S. B-52 bombers are drawing the "diplomatic wrath" of Beijing.

“If it was 20 years ago and they had not militarized those features there, it would have just been another bomber on the way to Diego Garcia or whatever,” Mattis said.