In my estimation, there’s only one presidential candidate in 2016 fully capable of doing the job, and she’s anything but a natural.

As Hillary Clinton has also been the target of maybe the longest-running smear campaign in American history — including roughly a dozen partisan Congressional investigations and a six-year leak-o-matic “independent counsel” probe led by the fastidious Kenneth Starr — it’s no wonder some voters mistrust her.

Overcoming that suspicion is her biggest challenge.

Republicans have predicted her imminent indictment for 20 years. You’d think by now they’d have made something stick, if there was anything to it. But it didn’t happen then, and it’s not going to happen now for an obvious reason: in a democracy, political show trials endanger the prosecution as much as the defense.

Anybody who watched Hillary’s one-woman demolition of Rep. Trey Gowdy’s vaunted Benghazi committee should understand that.

Meanwhile, one of the best things about Sen. Bernie Sanders’ presidential campaign is his unwillingness to smear his opponent. Too bad many of his most passionate supporters aren’t so fastidious. With Iowa’s make-or-break moment approaching for Sanders, it’s getting nasty out there.

It’s not so much the tiresome attacks on anybody who disagrees with them as a corrupt sellout. (My corporate overlords, of course, dictated that sentence.) It’s the seeming belief that people can be browbeaten into supporting their guy.

Some are a bit like Trump supporters–although normally without the threats. That too may be changing. Recently a guy visited my Facebook page saying people like me deserve “to be dragged into the street and SHOT for…treason against not only our country and our people, but the ENTIRE [BLEEPING] WORLD.”

My response — “Settle down, Beavis” — sent him into a rage.

But no, Hillary’s not an instinctive performer, although her stage presence strikes me as improved since 2008. A person needn’t be “inauthentic” (pundit-speak for “bitch”) to be uncomfortable in front of an audience.

As for authenticity, few Democrats could work a crowd like North Carolina Sen. John Edwards.

President Obama nailed it during a recent Politico interview:

Hillary does better with “small groups” than big ones, he observed, before putting his thumb heavily on the scale. He described Hillary as a fighter, who’s “extraordinarily experienced — and, you know, wicked smart and knows every policy inside and out — [and] sometimes [that] could make her more cautious, and her campaign more prose than poetry,” he said.

Even so, she came closer to defeating Obama in 2008 than Republicans have. “Had things gone a little bit different in some states or if the sequence of primaries and caucuses been a little different,” the president said, “she could have easily won.”

Indeed. As non-endorsements go, the president’s remarks couldn’t have been more complimentary. “She had to do everything that I had to do, except, like Ginger Rogers, backwards in heels,” he added.

Obama wisely said nothing critical about Bernie Sanders, but nothing particularly warm either. “Bernie came in with the luxury of being a complete long shot and just letting loose,” he observed. The president said he understood the appeal of Sanders “full-throated…progressivism.”

Well, Mr. Hopey-Changey as Sarah Palin calls him, certainly should.

Seven years of trench warfare with congressional Republicans, however, have brought out the president’s inner pragmatist. Which Democrat is best-positioned to consolidate the Obama legacy and move it forward?

First, one who stands a good chance of being elected.

Look, there’s a reason Karl Rove’s super PAC is running anti-Hillary TV ads in Iowa. Bernie Sanders “radical” past makes him a GOP oppo-research dream. Never mind socialism. Did you know he once wrote a column claiming that sexual frustration causes cervical cancer?

That in the 1970s, he called for nationalizing oil companies, electric utilities, and — get this — TV networks? Asked about it, he deflects by noting that Hillary once supported Barry Goldwater. Yeah, when she was 16. Bernie was in his mid-30s when he called for confiscating the Rockefeller family fortune. How most Americans hear that is: if he can take away their stuff, he can take away mine.

Sure, many people went off the rails during the Seventies. Most aren’t running for president. Bernie strikes me as a fine senator and a decent man. However, the current U.S. Congress has voted 60 times to repeal Obamacare. And he’s going to give us single-payer “Medicare for all?”

No, he’s not. Assuming he could find a sponsor, it’d never get out of committee. I doubt I’ll live to see single-payer health insurance in the USA. And I’m younger than Bernie. A complete retrofitting of American health care simply isn’t in the works. The votes just aren’t there, and they won’t materialize by repeating the magic word “revolution.”

President Obama says Hillary represents the “recognition that translating values into governance and delivering the goods is ultimately the job of politics, making a real-life difference to people in their day-to-day lives.”

Hard-won reality, that is, as opposed to fantasy.

Photo: Democratic presidential candidates Hillary Clinton (L) and Bernie Sanders (R) smile at the crowd following the First in the South Presidential Candidates Forum held at Winthrop University in Rock Hill, South Carolina November 6, 2015. REUTERS/Chris Keane