President Trump should ratchet down his rhetoric and learn to live with a nuclear North Korea, according to Susan Rice, national security adviser under President Obama.

In an op-ed for the New York Times, Rice said it's too dangerous for Trump to risk military engagement with North Korea with his "bluster," which could put millions of people in Seoul at risk. While she said the Trump administration should not "legitimize" North Korea as a nuclear state, it should start tolerating the new reality.

"History shows that we can, if we must, tolerate nuclear weapons in North Korea — the same way we tolerated the far greater threat of thousands of Soviet nuclear weapons during the Cold War," she wrote. "It will require being pragmatic."

Rice said the U.S. should make it clear that any use of nuclear weapons against the U.S. or its allies, or the transfer of nuclear weapons to third parties, would "result in annihilation of North Korea."

But she said the second step is for Trump to end his tough guy rhetoric in order to avoid "blundering into a costly war."

"John Kelly, Mr. Trump's chief of staff, must assert control over the White House, including his boss, and curb the Trump surrogates whipping up Cuban missile crisis fears.

She also criticized the "bluster" emanating from both Pyongyang and Bedminster, N.J., where Trump is staying for most of August.

Rice also recommended boosting its antimissile defenses, tightening sanctions against North Korea even further, and opening up talks with China about ways to negotiate down North Korea's arsenal.