It’s the bedrock principle of community organizing: Power comes from organized people and organized money.

Nobody understands this better than President Barack Obama, the onetime community organizer whose knack for rallying the masses and their money propelled him twice to the Oval Office.

So it’s telling when the power fades and the nucleus of Obama’s power source — labor unions — begins to turn against him, specifically against his far-reaching health care agenda. The chorus of labor opposition has grown to include even the federal workers charged with overseeing the financial segments of the massive Affordable Care Act.

The nation’s three largest labor organizations wrote recently to Democratic Senate Majority Leader Harry Reid and House Minority Leader Nancy Pelosi, complaining the Affordable Health Care Act — ObamaCare — would “shatter . . . our hard-earned health benefits.”

The writers — Teamsters President James P. Hoffa, United Food and Commercial Workers International President Joseph Hansen and UNITE-HERE President Donald “D.” Taylor — expressed their sense of betrayal over a broken promise to honor their unions’ employer-sponsored health care programs.

“Sadly, that promise is under threat,” their letter states. “We have been strong supporters of the notion that all Americans should have access to quality, affordable health care. We have also been strong supporters of you. In campaign after campaign we have put boots on the ground, gone door-to-door to get out the vote, run phone banks and raised money to secure this vision. Now this vision has come back to haunt us.”

Last week, federal employees joined the labor protests against the threats to their existing health plans. Under current provisions, federal workers get subsidies — vouchers — which they apply to a generous menu of federally sponsored health insurance options. But H.R. 1780, a bill introduced by Rep. Dave Camp, R-Mich., would do away with that practice, requiring instead that all federal employees be covered by exchanges under ObamaCare. Camp proposed the measure after reports surfaced that federal workers were seeking an exemption from the Affordable Health Care Act.

Among the new opponents is the National Treasury Employees Union, whose members include Internal Revenue Service workers — the very people charged with enforcing ObamaCare and collecting the hundreds of millions of dollars to make it go. NTEU’s website urges IRS agents to write Congress and oppose H.R. 1780.

Open enrollment is just two months away for the first phase of ObamaCare; implementation is to begin Jan. 1. Yet the vast majority of Americans still don’t understand it, many distrust it; and now labor unions are distancing themselves from it, including the union whose members are supposed to collect its operating revenues.

President Obama has spent the better part of three decades practicing and perfecting the strategies of community organizing, strategies that continue to serve him well in the political arena. He has demonstrated his command of power derived from his organization of people and their money.

Now Obama risks his political clout on the future of government-subsidized health care. It is the culmination of his life’s work. Its outcome will be his legacy.