IT’S BAD ENOUGH that a tyrant is testing American democracy. Now, an oligarch is trying to buy the presidency.

Michael Bloomberg’s net worth is more than $60 billion. The yearly return on $60 billion is at least $2 billion, which is what Bloomberg said he’ll pour into buying the highest office in the land.

In January alone, Bloomberg spent more than $300 million on campaign advertising. That’s more than Hillary Clinton spent during her entire presidential run. It’s multiples of what all other Democratic candidates have spent on advertising including billionaire Tom Steyer.

Bloomberg has already spent more on Facebook ads than Donald Trump, and more than Joe Biden, Elizabeth Warren, Bernie Sanders and Pete Buttigieg combined. His paid campaign staff is three times as large as Trump’s and five times as Biden’s.

The heart of Bloomberg’s campaign message is that he has enough money to blow Trump out of the water. To demonstrate this, Bloomberg bought a $10 million Super Bowl ad that slammed Trump in the middle of the big game and he bashed Trump in a national ad appearing just hours before Trump’s State of the Union address.

If Trump’s angry tweets are any barometer, Bloomberg’s tactics are getting under the thin-skinned president’s fragile epidermis.

Meanwhile, the Democratic National Committee is putting Bloomberg on the debate stage by abandoning the individual-donor threshold that it used for the first eight debates; presumably because Bloomberg isn’t taking donations.

To participate in the debate in Las Vegas, Nev., Democratic candidates had to show at least 10% support in polls. Bloomberg’s wall-to-wall advertising gave him a good shot. Feb. 3, he tied with Warren in third place in Morning Consult tracking poll. He’s in the top four in many Super Tuesday states.

Bloomberg has some attractive policy ideas. He’s for gun control, wants to reverse climate change and seeks to raise an estimated $5 trillion of new tax revenue from high earners and corporations including a repeal of Trump’s 2017 tax cuts and a new 5% surcharge on incomes more than $5 million a year.

But Bloomberg also is a champion of Wall Street. He fought against the reforms following the near meltdown of the Street in 2008. His personal fortune is every bit as opaque as Trump’s. Through his dozen years as mayor of New York, he refused to release his federal tax returns. Even as a candidate for president, he still hasn’t given a date for their release. And, remember, he’s trying to buy the presidency.

America has had some talented and capable presidents who were enormously wealthy; Franklin Roosevelt, Theodore Roosevelt and John F. Kennedy for example.

The problem lies at the nexus of wealth and power, where those with great wealth use it to gain great power. This is how oligarchy destroys democracy.

Oligarchy comes from the Greek word oligarkhes, meaning few to rule or command. It refers to a government of and by a few exceedingly rich people.

Since 1980, the share of America’s wealth owned by the richest 400 Americans has quadrupled, while the share owned by the entire bottom half of America has declined. The richest 130,000 families now own nearly as much as the bottom 90%, 117 million families, combined. The three richest Americans own as much as the bottom half of the population. Bloomberg is the eighth-richest person in the United States.

Much of this money has found its way into politics. In the election cycle of 2016, the richest 1/100th of 1% of Americans accounted for a record-breaking 40% of all campaign contributions.

Unlike income or wealth, power is a zero-sum game. The more of it at the top, the less of it anywhere else.

A half-century ago, when America had a large and growing middle class, those on the left wanted stronger social safety nets and more public investment in schools, roads and research. Those on the right sought greater reliance on the free market.

But as power and wealth have moved to the top, everyone else, whether on the old right or old left, has become disempowered. Today, the great divide is not between left and right. It’s between democracy and oligarchy.

Bloomberg is indubitably part of that oligarchy. This should not automatically disqualify him, but it should set off alarms. If the only way we can get rid of the sociopathic tyrant named Trump is with an oligarch named Bloomberg, we will have to choose the oligarch.

I hope it doesn’t come to that. Oligarchy is better than tyranny, but neither is as good as democracy.

Robert Reich’s new book “The System: Who Rigged It, How We Fix It,” will be available in March.