“Imagine what would be possible right now with ideas that are bold enough to meet the challenges of our time, but big enough, as well, that they could unify the American people [like the 9/11 attacks did],” said South Bend, Indiana mayor Pete Buttigieg in his opening statement at the Sept. 12 Democratic presidential nomination debate. “That’s what presidential leadership can do. That’s what the presidency is for.”

Sen. Kamala Harris, D-Calif., said she plans on “unifying the country” as president too.

“I know what’s broken. I know how to fix it,” Sen. Elizabeth Warren, D-Mass., assured us as she applied for the job of running nearly every aspect of our lives.

The other candidates, and most if not all recent presidents, display the same symptoms of — there’s really no other term for it — narcissistic megalomania.

If you’re going to go to the trouble of running for president, a good first step might be to crack open a copy of the U.S. Constitution and find out precisely what, as Mayor Pete says, “the presidency is for.”

In simple terms, it goes something like this:

Congress, supposedly within rigid confines also set forth in the Constitution, legislates. The president’s job is to execute Congress’s will.

Yes, the president has veto power, but Congress can override a presidential veto with a vote of two-thirds of both houses.

Yes, the president is commander in chief of the armed forces, but only when they are “called into the actual Service of the United States,” which is when Congress declares war (the founders frowned on standing armies).

Yes, the president appoints executive branch officials to carry out Congress’s instructions, but the highest of those officials have to be confirmed by the Senate. Ditto the Supreme Court justices who referee disputes of law.

Yes, the president can negotiate treaties, but once again, those treaties have to be ratified by the Senate to become law.

The presidency is not “for” weird schemes to “unify the country” with “bold” and “big” ideas. It’s not the president’s job to figure out what’s “broken” and “fix it.”

The president, under the Constitution, is not “in charge.” He or she is a functionary with extremely limited powers.

But the Constitution has clearly become passe. Congress has (unconstitutionally) handed over much of its power to the executive branch and (dysfunctionally) failed to wisely exercise what little power it still claims.

We’re most of a century into what some call the age of the “imperial presidency” — America’s sickening descent to the status of banana republic.

No wonder candidates for the presidency act like they’re running for Mom or Dad of Everyone.

“[W]hether the Constitution really be one thing, or another, this much is certain,” wrote 19th century anarchist Lysander Spooner: “That it has either authorized such a government as we have had, or has been powerless to prevent it. In either case it is unfit to exist.”

American politics routinely confirms that diagnosis.

The Constitution is dead. It’s time to start over from scratch.