Stanley McChrystal, a top retired general and Biden adviser, tells Axios that "China's military capacity has risen much faster than people appreciate," and the U.S. is running out of time to counterbalance that in Asia and prevent a scenario such as it seizing Taiwan.

Why it matters: McChrystal, the former commander of U.S. and NATO forces in Afghanistan, recently briefed the president-elect as part of his cabinet of diplomatic and national security advisers. President-elect Joe Biden is considering which Trump- or Obama-era approaches to keep or discard, and what new strategies to pursue.

• In the interview, McChrystal said a nuclear-armed North Korea is still the most pressing national security threat — just as President Obama warned President-elect Trump in late 2016 — and "there's no negotiating them away" from being a nuclear power despite Trump's flashy efforts.

Asked whether it's too late for the U.S. to marshal Asian allies to deter China, McChrystal said, "I think that, if the ship hasn't sailed, it's certainly got up steam and thinking about sailing."

The big picture: McChrystal sounded the alarm about China's stealthy military buildup and signaled that the Biden administration cannot afford to be complacent about that dimension of the China threat.

• "Their ability with rocketry and whatnot has essentially changed the dynamic," McChrystal said. China has touted hypersonic missiles that could sink a U.S. aircraft carrier.
• He added that the U.S. must invest more in the capability of its forces and regional alliances, in part to forestall a move on Taiwan — a breakaway island that China claims.
• "My concern would be, we wake up one morning and China has just done a fait accompli," he said. "They have just showered Taiwan with rockets."
• The question then: "Are you really prepared to fight for Taiwan?"

Between the lines: Given his history, few might have expected McChrystal to endorse Biden, or become an informal adviser.

• President Obama fired him in 2010 after a Rolling Stone reporter quoted McChrystal and his aides speaking disrespectfully about government officials, including then-Vice President Biden.
• But as Rolling Stone now notes, Obama writes in his new memoir that he liked McChrystal and was conflicted about firing him.
• Biden's team embraced McChrystal’s endorsement during the campaign.

What's next: The U.S. must invest in building a ring of Southeast Asian and other Asian allies, and it must think and act like an Asian power itself, McChrystal said.

• When it comes to North Korea, he added: "The best you can do is a little bit like the Cold War, is, manage this thing."
• Any war to stop them would be "very bloody," whether it had a nuclear component or not.

The bottom line: "I think there's enough of a possibility that over time, probably 20 years, you manage this thing a little bit like the fall of the Soviet Union," McChrystal said of North Korea.