Let’s assume that Hillary Clinton was serious the other day when she said that excessive partisanship was taking America “backwards.” That means she’s on the phone right now reading the riot act to fellow Democrats Harry Reid and Chuck Schumer.

Yeah, right.

Clinton’s pose of rising above the political scrum made for a good headline just as her party is plumbing new depths of mud and smears. Reid and Schumer are tarring David and Charles Koch in ways that smack of McCarthyism, though Tail Gunner Joe at least found a few real Communists.

Reid, a nasty little man who demeans the office of Senate majority leader, called the Koch brothers “un-American” because they dare to spend their own money advancing causes he doesn’t like. Reid, of course, spends public money advancing causes the public doesn’t like.

Schumer, hoping to succeed Reid, obviously thinks the way to success is to ape his mentor’s worst instincts. In the process, he proves the adage that sometimes, party asks too much, though it’s hard to know where party ends and personal ambition begins.

Most New Yorkers who pay close attention no longer think of Schumer as their senator. He belongs to Washington, his Sunday press conferences in the city designed to suggest he hasn’t forgotten actual voters. But having spent his whole life in politics, federal power is the coin of his realm and the mint is on the Potomac, not the Hudson.

Sometimes his ambition comes at the expense of New York, his attacks on the Koch brothers being the latest and most glaring example. David Koch has given some $619 million to charitable causes in Gotham, and for this, Schumer treats him like Public Enemy No. 1.

“The Koch brothers aren’t just sitting there innocently on the side,” Schumer said on TV in defense of the party’s strategy of turning the brothers into modern Reds. “They’re spending ­­$40, $50 million in ads that are not focused on their real agenda . . . So I don’t feel sorry for them.”

Beyond being oblivious to his childish tone of “they hit us first” and the unseemly spectacle of government power being used to punish private citizens for exercising their First Amendment rights, Schumer did voters a favor by removing any pretense of substance. He effectively conceded that the anti-Koch campaign is pure politics, divorced from any social good.

Veering into war-room talk usually kept secret, he cited polls showing that 48 percent of Americans recognize the Koch name, and the party’s aim to drive up that number by the midterm elections.

“That’ll mean about 90 percent of them will know it in October,” Schumer said in the interview. “We also have to have a shield that protects us from these ads. And I think the Koch brother thing will work.”

See, the attacks are a “thing” that “will work.” Not, mind you, for New Yorkers or any ordinary American. He believes the ads “will work” to keep Dems in charge of the Senate and give him a chance to be majority leader.

If the Koch brothers decide to stop giving away their money, or if their businesses shrink and people lose their jobs, well, that’s all part of the price ordinary people must pay for their leaders’ ambition.

All that would seem to qualify as the kind of excessive partisanship Clinton laments, but she’s not likely to break ranks with the flamethrowers. Indeed, hubby Bubba once complained of the “politics of personal destruction” even as he was becoming a master of it, and there’s no evidence she intends a more dignified approach.

No matter the era or the party, pols who go down that rabbit hole are conceding they have no solutions to offer voters. And that’s exactly where the Democratic Party is now.

Six years of Obamaism have left America polarized at home and a laughingstock abroad; Hillary Clinton, Reid and Schumer all have played starring roles in that disaster.

They hung Israel out to dry and helped fashion the domestic policies, including ObamaCare, that are as unsuccessful as they are unpopular. Now that they’ve run out of ideas and gas, all they have to offer is a plan to destroy their fellow citizens.

And they call others “un-American.”

Toothless US spells no trouble for Putin

That John Kerry — what a joker. With Russia showing signs it will bite off another piece of Ukraine, our secretary of state warned that Vladimir Putin will face “further costs” if he takes one more step.

“Further costs” suggests Putin paid a price for gobbling up Crimea. Beyond Kerry’s insistent finger-wagging, can anyone identify that price?

Me neither.

Uh, look in the mirror, Al

Al Sharpton, defending himself against a report that he was a secret FBI informer 30 years ago, aimed an especially low blow at the authors. “They’re just trying to get some attention,” he said.

Wow, imagine if that were a crime.

G-$tringing us along

The story about the Long Island nursing home that invited male strippers in to entertain the residents is probably going to get worse before it goes away. No doubt we’ll soon learn that Medicaid paid the tab, with the charges billed as “physical therapy.”

Dinap all over map

It’s official — Tom DiNapoli lacks the courage of his convictions. The state comptroller was a leader for years in demanding public financing of campaigns, but when his bluff was called, he folded like a cheap suit.

DiNapoli is turning down an offer he solicited. At his request, Gov. Andrew Cuomo and legislative leaders gave him what he wanted, but apparently not exactly the way he wanted it. As a test, they approved public financing only for the comptroller’s race this year, and promised to commit $24 million in taxpayer money for matching funds.

But DiNapoli, acting like the princess who can’t sleep with a pea buried under her thick mattress, said no, thanks. Well, actually, he just said no.

He called the test program a “poor excuse” for the real thing and said, “I was always willing to have reform start with the Comptroller’s Office, but I will not be a convenient sacrificial lamb.”

Tsk, tsk. His real objection probably has something to do with the fact that, under the new rules, he would have to return or set aside nearly 75 percent of the $2.1 million of contributions he has in the bank. That would wipe away any advantage of incumbency and give a Republican challenger a better shot at beating him. In that case, then, reform can wait.

Still, Cuomo, revealing a puckish sense of humor, expanded his offer and said he was willing to change the rules to ones DiNapoli finds more convenient.

That sounds like a dare, but I’m guessing DiNapoli will find another reason to say no. Principles are good, but keeping his job is better.