Trying to create a presidential persona and a rationale for running, Hillary Clinton relaunched her campaign at a memorial to FDR. She used the glorious setting of Four Freedoms Park to summon Roosevelt’s legacy and frame her theme as “Four Fights.”

She also invoked her husband and President Obama, as if piggy-backing on presidents would define her. Perhaps it will work, but her predicament recalls a Dem president she didn’t mention: Lyndon Baines Johnson. The similarities must scare her.

LBJ looked certain to be re-elected in 1968, until a Minnesota senator with a penchant for poetry named Eugene McCarthy shocked the world by getting 42 percent in the New Hampshire primary, against Johnson’s 49 percent. Less than three weeks later, the president famously declared that “I shall not seek, and I will not accept, the nomination of my party for another term as your president.”

If there is a McCarthy-like figure on the scene today, it is Bernie Sanders, the scrappy underdog threatening to upset Hillary’s coronation.

The news that Sanders is surging in polls in Iowa and New Hampshire must be sending shivers through Clinton’s camp. Even though Hillary still leads in the 2016 first states, the gap has narrowed so much that her surrogates are lowering expectations, saying Sanders might win some showdowns.

That’s amazing enough, but her problem could be even more serious. Echoing the Mark Twain line that “history doesn’t repeat itself, but it does rhyme,” the Clinton-Sanders dynamic is starting to rumble like the political earthquake of ’68.

LBJ’s demise is a textbook example of how quickly the bubble can burst. He had the power of incumbency while Hillary wears the mantle of inevitability. That didn’t work for her in 2008, either, when Obama emerged to crash her party.

Sanders, a self-described democratic socialist, doesn’t need to win the nomination — and he probably won’t — to block Clinton. He only need show that she’s not inevitable, and that there is a motivated, significant piece of the party that rejects her.

That is exactly what he’s doing, as large, enthusiastic crowds greet him wherever he goes. If she looks beatable, more viable candidates will find the courage to run.

That’s the McCarthy model. He ran as a dissident against the Vietnam War and the New Hampshire results in mid-March of ’68 crystallized unhappiness with Johnson.

Nearly 20,000 American soldiers were dead by the end of 1967, and the election year would be the bloodiest of all. It started with a Jan. 1 attack on a US military base and February’s Tet Offensive saw the deadliest single week of the war, when 543 Americans were killed and more than 2,500 wounded. Overall, 16,899 of our soldiers died in 1968, the most in any year.

In those dark days, many people, including top Democrats, grew disillusioned with Johnson, and McCarthy’s promise to end the conflict found special resonance among draft-age students. Shaggy anti-war protesters shaved and got haircuts in a “clean for Gene” movement.

But the New Hampshire primary was McCarthy’s high-water mark. Bobby Kennedy jumped in and, after Johnson bowed out, so did Hubert Humphrey. Kennedy probably would have won, but was assassinated in June by Palestinian terrorist Sirhan Sirhan. Humphrey got the nod at the Chicago convention, a debacle marked by violent street protests that helped Republican Richard Nixon win the presidency.

For her part, Clinton already has veered left to head off a challenge from the progressive flank. But her long record as a relative military hawk who is cozy with Wall Street is proving a tough sell in a party increasingly more radical than she is.

The anti-Hillary movement is also picking up steam because of her shady dealings with international oligarchs and the rivers of cash flowing to the Clinton Foundation. Never reliably honest, she’s been caught in lies about her e-mails as secretary of state, leading most voters to say she is untrustworthy. That, in turn, is keeping several GOP candidates ahead or close in hypothetical matchups.

Although she remains the likely nominee, there are many dents in Clinton’s armor and a long way to go. By the end, 2016 could be the new 1968.

Bratton is better than his word

Bill Bratton’s bite is worse than his bark. That’s a very good thing for New York.

With crime in June falling to its lowest level since at least 1993, the top cop is showing he still has a talent for miracles. Through May, murder was up nearly 20 percent.

Bratton’s reaction then was a disappointment, writing in The Post that the “relatively minor increase” did not mean crime was “raging out of control.” He said he had a plan of action, but his lack of a clear promise sounded like he was preparing the city for a new normal of more violence.

Thankfully, that has not happened. June’s numbers were dramatically lower than a year ago, with murders down 38 percent and fewer shootings, rapes, robberies and stolen cars.

Beyond the obvious benefits, the stats are comforting because they prove the NYPD still can move quickly and make a life-saving difference despite the handcuffs and insults coming from City Hall. It’s just one month, but let’s hope this is the start of a new, downward trend.

Congratulations to the commissioner and all the members of the NYPD. Once again, they showed why they are the Finest.

Smith’s old wives tale

Former state Senate leader Malcolm Smith had delusions of grandeur, boasting that he, President Obama and Gov. David Paterson all had wives named Michelle. The implication was that he, too, was bound for glory.

His sentencing on federal bribery charges brought him back to earth with a thud. A Democrat, he was convicted of a scheme to buy his way onto the Republican mayoral ballot in 2013.

Leaving court last week, Smith said only, “I thank God for the opportunity I’ve had to serve.” Presumably, he didn’t mean his time in prison, which was set at seven years.

Oh, how the would-be mighty have fallen.

Pataki plays his ‘Trump’ card

Who’s afraid of Donald Trump? Apparently most of the GOP presidential candidates except George Pataki.

Even as Republicans try to attract Latino voters, the former three-term New York governor broke the party’s shocking silence over Trump’s statement that Mexican immigrants are “bringing drugs. They’re bringing crime. They’re rapists.”

In an open letter to competitors, Pataki said the comments “left me and a lot of other sensible people wondering what century we are living in,” and urged others to join him in denouncing them.

Initially, only former Texas Gov. Rick Perry mumbled disagreement, but late Friday Marco Rubio finally denounced Trump’s comments as “offensive.” And yesterday, Jeb Bush chimed in, labeling Trump’s remarks “extraordinarily ugly.” Better late than never.

Pataki is a long shot for the nomination, but his refreshing capacity for decency has not been dimmed by his time out of office.