President Donald Trump's longest-serving national security adviser John Bolton condemned his presidency as dangerously damaging to the United States and argued the 2020 election is the last "guardrail" to protect the country from him.

In an exclusive interview with ABC News, Bolton offered a brutal indictment of his former boss, saying, "I hope (history) will remember him as a one-term president who didn't plunge the country irretrievably into a downward spiral we can't recall from. We can get over one term -- I have absolute confidence, even if it's not the miracle of a conservative Republican being elected in November. Two terms, I'm more troubled about."

In the interview with ABC News Chief Global Affairs Correspondent Martha Raddatz and in his new book, "The Room Where It Happened," Bolton paints Trump as "stunningly uninformed," making "erratic" and "irrational" decisions, unable to separate his personal and political interests from the country's, and marked and manipulated by foreign adversaries.

"I don't think he's a conservative Republican. I'm not going to vote for him in November -- certainly not going to vote for Joe Biden either. I'm going to figure out a conservative Republican to vote in," he told Raddatz.