John Bolton — Donald Trump's former national security adviser — is laying out his nightmare scenarios for a second Trump term in a foreword to the paperback edition of his memoir "The Room Where It Happened," out Tuesday.

Why it matters: Bolton writes that "a mountain of facts demonstrates that Trump is unfit to be President."

• In the 18-page foreword, "The Room Where It Will Happen Again," Bolton worries Trump could pull the U.S. out of NATO, abuse power to exact retribution on political rivals and trigger a constitutional crisis.

Zoom in: Bolton reserved his most damning predictions for foreign policy. He wrote that Trump could:

• Throw Ukraine under the bus to favor Russian President Vladimir Putin.
• Endanger Taiwan's independence and embolden China.
• Reunite with North Korea's Kim Jong-un.
• Seek a bad deal with Iran driven by his desire to prove himself a master negotiator.

"Indeed, it is a close contest between Putin and Xi Jinping, who would be happiest to see Trump back in office," he writes.

Trump campaign spokesperson Jason Miller told Axios: "For someone who professes to have such great disdain for President Trump, 'Book Deal Bolton' sure has found a way to grift off the relationship."