How far left has the Democratic Party turned? Well, Mike Bloomberg aims to become the main “moderate” rival to frontrunner Bernie Sanders — yet Bloomy’s promising to raise taxes by $5 trillion over a decade.

When we encouraged Bloomberg to join the race over a year ago, it was because he had “declared his intention to run as a moderate in an effort to pull the Democratic Party back to the center.”

Sigh: Now he’s vowing tax hikes higher than Joe Biden’s plan for a $3.4 trillion hit.

Yes, it’s less than Liz Warren’s call for new federal revenues of $30 trillion, and the even-higher (we’ve lost count) plan from Bernie Sanders.

But Hillary Clinton in 2016 proposed hikes of “just” $1.4 trillion. And Barack Obama in 2008 vowed to hike taxes on the rich while overall cutting them by $2.9 trillion.

Obama was the left-wing candidate then — yet his position would get him laughed off the Democratic debate stage in 2020. That’s how far the party’s base has shifted, driven by Sanders — a socialist who isn’t even a member of the party except when he’s running for president.

Mind you, most Democratic office-holders know this is general-election suicide: Just two years ago, 79 House Democrats voted against the Congressional Progressive Caucus budget that aimed to hike taxes by $9 trillion over 10 years — and that was before the 2018 elections, when dozens of new moderate members won by appealing to the center.

And so would-be “moderate” Bloomberg aims to starkly raise tax rates on corporations, investors and individual high earners, not only rolling back many of the Trump tax cuts but boosting estate and capital-gains taxes while creating a 5% “surtax” on incomes over $5 million a year.

And his advisers say he might come up with even more revenue-raising measures — and specifically said he didn’t see the current $1 trillion deficit as an issue.

Which suggests that he’ll also be offering spending plans that compete with the other candidates, who are calling for trillions to go for a Green New Deal, Medicare for All and so on.

Yes, Mike Bloomberg has been a liberal his whole life, only registering temporarily as a Republican so he had a path to run for mayor of New York City. He’s always been pro-gun control and long wanted to spend big to combat global warming.

But he’s abandoning other principles for this run — witness his complete 180 on stop-and-frisk and now his tax-hike fever. Will he come out against charter schools next?

A year ago, it looked like Democrats had a pretty good chance of beating President Trump this November. Now their race to the left seems designed to hand him a second term.