Hillary Clinton is doing the country a great service.

By making it clear she is going to run for president as an unapologetic left-liberal — with emphasis on the “left” — she has made sure that the 2016 election will be exactly the referendum on America’s future it ought to be.

She did not have to make this choice. Polls show that despite two months of problematic stories about destroyed emails and discomfiting revelations about the behavior of the foundation that bears her last name, she remains wildly popular among Democrats.

That fact should give her all the running room in the world — and usually when presidential candidates have running room, they run as fast to the center as they possibly can.

Certainly that is what Republicans running for president still think. In fact, the so-called “first-tier” GOP candidates — Jeb Bush, Marco Rubio and Scott Walker — are attractive precisely because they seem to have a sense of how they and their party need to reach beyond the conservative movement and the Republican base to secure victory in November 2016.

Not so, Hillary. When she made her dramatic announcement on Tuesday that she would seek full citizenship for illegal immigrants, she was also announcing that she and her team no longer think the old rules of presidential politics apply.

The same could be said of her radical speech last week at Columbia University on criminal justice issues, when she said the nation needed to turn to the kind of leadership David Dinkins had provided as mayor of New York City while effectively endorsing what might be called a new “softer on crime” approach.

So much for the notion that she would run as a kind of nostalgia candidate committed to bringing back the glory days of the 1990s, when Bill Clinton signed crime bills and defense-of-marriage acts and balanced the budget with Newt Gingrich in tow.

Hillary spent some time last year testing out a strategy of distancing herself somewhat from Barack Obama, especially on foreign policy, but now seems to have discarded it entirely. She is running as an Obama Democrat, full throttle.

This is not the Hillary we saw in 2007 and 2008 (and for good reason, since that Hillary lost to Barack Obama).

In that earlier election, she embraced the conventional wisdom that a successful national candidate had to broaden her appeal beyond the activist groups of her party and make herself palatable to voters who are up for grabs in the general election.

Now she is taking a leaf from the Obama 2012 playbook — which makes sense, not only because he won in 2012 but because she is relying on Obama stalwart Joel Benenson and others from the Obama camp for strategic counsel this time.

What they did in 2012 was to dig as deeply as possible into their own Democratic soil and try to harvest all their votes from it. This was not a broad-based approach; it was a concentrated and focused approach. They cultivated their own.

It proved a sound strategy because in 2008 the partisan composition of the electorate had Democratic voters at around 39 percent and Republicans around 30 percent.

The Obamans knew if they could just get every Democrat who had voted for Obama in 2008 to vote for him again, he would win — even if independents went for Mitt Romney. Which they did, by 5 points. No matter. Nor did it matter that Obama got 4 million fewer votes in 2012 than he had in 2008. He won easily nonetheless.

The question is whether Hillary’s candidacy will be able to generate that kind of response among Democrats — especially among African-Americans, who voted almost unanimously for Obama and at a higher overall rate of 66 percent than white voters at 64 percent. But it looks like she’s determined to try.

And trying means running to the left — perhaps even farther to the left than Obama, who is already the most left-wing president we’ve ever had.

She will be presenting Americans with a clear and unambiguous choice.