The rapid pace of change in American life does not exempt politics. Witness how fast Democrats are cycling through scapegoats.

First came Hillary Clinton. When she emerged to gripe about all the reasons she lost last year, except herself, party activists told her to be quiet and go away. She has, for now.

Next came Nancy Pelosi. When Republicans won four contested special elections for House seats, disgruntled Dems turned their fire on their minority leader, telling Pelosi it was time to get out of the way. She refuses, for now.

And now comes Barack Obama. The former president, shredding what was left of his promise not to interfere with his successor, is joining the fight against the repeal of ObamaCare. He called the Senate bill an example of “meanness,” and pledged to campaign for the Democrat in the Virginia governor’s race.

For Republicans, luck can’t get much better. While Clinton and Pelosi were hardly innocent bystanders in the historic rout of Democrats at every level of government, the main culprit was Obama.

It was Obamaism, more than Clintonism or Pelosism, that elected Donald Trump and gave the GOP both houses of Congress. The former president’s coercive liberalism at home and appeasement abroad led to the greatest upset in American politics.

His two biggest achievements, ObamaCare and the Iran nuclear deal, were sold on the backs of lies. President Trump is Obama’s legacy.

And now Dear Leader wants to “help” Dems again. Let’s see how many Clinton and Pelosi critics have the courage to tell him, “No, thanks, you’ve done enough.”

Obama’s desire to re-litigate his tenure comes amid other signs that the siege of the Trump White House is lifting and the political momentum is shifting.

Suddenly, Dems are the fighting, fractured party with no agenda or leader while Republicans finally show signs of uniting their majorities to get big things done.

Indeed, Obama’s return to the fray coincides with a belated congressional focus on his administration’s misconduct on the Clinton investigation and his failure to counter Russian interference in the election.

Most ominously, the Senate Judiciary Committee has opened a probe into whether former Attorney General Loretta Lynch impeded the FBI investigation into Clinton’s private email server, with members from both parties raising concerns about her role. They cited accusations by former FBI Director James Comey and a published report that Lynch promised a top Dem that she would not let the Clinton investigation go far.

It’s hard to believe Lynch won’t be forced to testify publicly, an event that would revisit all the suspect twists and turns of the Clinton probe, including Lynch’s failure to impanel a grand jury. She also should be asked what, if any, orders she got from a White House invested in a Clinton victory.

The role of politics also surfaced when Obama’s former director of homeland security admitted that the administration decided to withhold public discussion about Russian hacking because of its possible impact on the campaign.

“This was a big decision, and there were a lot of considerations that went into it,” Jeh Johnson told the Senate. “This was an unprecedented step.”

He said the White House feared that accusing Russia of interference might have looked like an effort to help Clinton, especially given Trump’s claim that results would be “rigged.”

Obama’s decision to wring his hands and take no action until after the election, when he imposed minor sanctions on individual Russians, might explain his team’s efforts to pin the collusion tag on Trump. Those charges, made mostly by anonymous leaks, are catnip to the Democratic media and distract attention from Obama’s failure to respond to what has been described as a Russian act of war.

Taken together, last week’s extraordinary developments are injecting a dose of reality into the Washington scandal machine. For months, anonymous-sourced reports about various Trump associates having meetings with Russian officials painted a troubling picture and led to the appointment of a special counsel.

But when the Obama team’s role is highlighted, it too looks very troubling. The implications of the president being paralyzed because he didn’t want to give Trump ammunition are almost as grave as the still-unexplained surveillance, leaks and unmasking of Trump associates.

From here, it all looks like the Obama White House is guilty of playing politics with national security.

The possibility is worthy of special counsel Robert Mueller’s attention, who is so far exclusively focused on Trump’s team. That one-dimensional view must end.

Because Russian interference has been used only as a partisan club against Trump, the seriousness of the issue has not resonated with the public. This was indeed an attack on our democracy, and all Americans have a stake in making sure it doesn’t happen again.

But public trust can be earned only when the partisan mud is scraped away and all the facts given a full and fair examination. That means no sacred cows from either party and either administration.

Can Washington handle the truth? We’re about to find out.

A whole Lhota love

The late Mayor Ed Koch was fond of saying that “public service is the noblest of professions if it is done honestly and well.”

He might have been talking about Joe Lhota’s latest gift to New York.

Lhota’s decision to come back to the beleaguered MTA and accept the part-time chairman’s role is public service at its finest. For his trouble, he will reap the windfall of $1 a year and more headaches than any human can bear.

Time and circumstance, including aged infrastructure and surging ridership, have thrown the subway system into crisis mode. The assumption that riders can get from here to there safely and reliably threatens to become a thing of the past, and that is perilous to the region’s economy and quality of life.

Lhota, agreeing to Gov. Andrew Cuomo’s request to return to the agency he left four years ago, has been careful not to promise a single, quick answer. While riders may be out of patience, Lhota deserves their thanks and trust as he begins the hunt for solutions.

Godspeed to him, and congratulations to New York for having such dedicated citizens.

Mayor & wife’s Miami vice

Generally, it’s safe to assume the city is better off when Mayor Bill de Blasio is out of town. There is less chance he’ll reward a donor, make a boneheaded decision or clog traffic with his SUV convoy.

But his taxpayer-funded trip to Miami is an exception. The Post reports he and first lady Chirlane McCray took 12 city employees, including a photographer, for a conference.

There is no legitimate excuse, especially for the entourage. It’s a vanity junket. Period.

This way and that

Block that metaphor.

An Upshot column in the New York Times includes this description of Democrats’ chances in 2018: “The problem is they’re going uphill, even if the wind is strongly at their backs.”