No longer a slouch when it comes to employing rhetoric, former New York City Mayor Michael Bloomberg defended his record of restoring fiscal sanity and his role in stabilizing the financial system with headlines trumpeting his accomplishments in office. Such words, he said, were necessary to escape the charges that had been thrown his way by the president.

But Mr. Bloomberg’s denunciations of Mr. Trump cast him more like a liberal Kennedy than a conservative George W. Bush. A Cuomoian Democrat, he has embraced gun control, championing a ban on assault weapons like the Bushmaster described in the Sandy Hook School shooting and proposing President Obama’s executive order requiring background checks on gun show and internet sales.

There is a lot to praise in Mr. Bloomberg’s advice on limiting government’s role in business and restraining the national debt, as well as the impact of his investments as the founder of private equity firm, Bloomberg L.P.

This is especially true of his emphasis on corporate governance — one of the classic liberal concerns. Again and again, he has advocated that company boards and CEOs have clear rules of behavior and be accountable to shareholders for their actions. This has never been my own view, although I’ve often found Mr. Bloomberg’s observations to be innovative.

His blanket praise of President Kennedy’s leadership in Cuba notwithstanding, Mr. Bloomberg seems fully to accept Mr. Kennedy’s view that each new administration is a corrective to the last. That is a key trait of liberal leadership, as George Will has often observed. To grasp the power of liberal Democratic leadership, you have to understand that America’s “first liberals” — Theodore Roosevelt, Franklin Roosevelt, Harry Truman and John F. Kennedy — were concerned with what they dubbed, respectively, the “four horsemen of the apocalypse,” the Cold War, the deficit and equality for minorities.

For example, then-Vice President Truman talked about the coming apocalypse caused by the menace of “industrial intermarriage” with factories and farms in close proximity. Mr. Roosevelt said it was only a matter of time before Communists would move into the schools and the cities. Mr. Truman asked: “What kind of country do we want to live in — where we’re all murdered by Communists in the schools, on the streets, in the clubs, in the laboratories and in the mines, or what?” When he ran for president, Mr. Trumbull pledged that “we won’t be stupid.” The horror and horror and horror of the minority tyrannies on communism — forced labor camps, enforced ignorance, surveillance of the political and religious dissenters — made great headway for liberalism.