Former President Barack Obama is jumping back into the spotlight, using his social media pulpit to campaign against the latest bid to replace the bulk of his signature health care law.

In a 939-word message to his 53 million Facebook followers, Obama declared the Senate’s newly unveiled ObamaCare replacement bill is “not a health care bill” but instead “a massive transfer of wealth from middle-class and poor families to the richest people in America.”

He urged Senate Republicans to “step back and measure what’s really at stake” before voting on the bill, which was unveiled Thursday. While blasting the proposal, he urged his allies to speak out against the “fundamental meanness at the core of this legislation.”

The Trump White House, however, shot back Friday that Republicans are acting because the Affordable Care Act has driven up costs and driven out insurers from markets across the country.

“The real meanness is allowing the American people to believe that ObamaCare is still alive,” White House Press Secretary Sean Spicer told Fox News' "America's Newsroom."

He added, “ObamaCare has failed. In county after county, they are left with no choices. Rising premiums and skyrocketing deductible. ObamaCare is dead.”

Moments after Obama made his Facebook post Thursday, President Trump tweeted his support of the Senate bill.

The high-stakes social media confrontation between a former president and a sitting one is rare and runs counter to Obama's own declarations of wanting to stay on the sidelines following his two terms as commander-in-chief.

During his last few days in office, Obama joked that he was looking forward to not hearing himself "talk so darn much."

"I want to be respectful of the office and give the president-elect an opportunity to put forward his platform and his arguments without somebody popping off," Obama said at a forum in Lima, Peru – but added that if an issue “goes to the core questions about our values and our ideals, and if I think that it’s necessary or helpful for me to defend those ideals, then I’ll examine it when it comes.”

In early May, Obama responded to late night host Jimmy Kimmel’s emotional plea to lawmakers to leave key ObamaCare provisions in place. Kimmel, speaking about his newborn son’s heart surgery, asked Congress to expand access to health insurance and to retain protections for people with pre-existing medical conditions.

Obama tweeted, “Well said, Jimmy. That’s exactly why we fought so hard for the ACA, and why we need to protect it for kids like Billy. And congratulations!”

Obama’s strong support of the Affordable Care Act, or ObamaCare, shouldn’t come as a surprise. Getting the ACA passed was the hallmark of his domestic policy agenda.

Still, GOP critics claim that in an effort to save his legacy, Obama is glossing over some very real problems with the health care bill that have led to health insurers pulling out of exchanges or imposing double-digit premium increases.

Senate Republicans on Thursday unveiled a draft version of their health care reform bill that cuts Medicaid, ends penalties for people not buying insurance and reshapes subsidies to low-income users.

The 142-page bill, which also prohibits states from opting out of key protections for patients with preexisting conditions, eliminates much of Obama’s legislation.

The measure would repeal tax increases Obama's law imposed on higher-income people and medical industry companies to pay for expanded coverage. And it would end the tax penalty Obama's statute imposes on people who don't buy insurance -- in effect, ending the individual mandate.