Former President Barack Obama said Wednesday there are no practical benefits to a bill Republicans are considering to replace the Affordable Care Act.
Speaking in New York, Obama said the bill would increase costs and strip coverage from vulnerable Americans.
"When I see people trying to undo that hard-won progress, for the 50th or 60th time, with bills that will raise costs, reduce coverage and roll back protections for older Americans and people with pre-existing conditions ... it is aggravating," Obama said during an event sponsored by the Bill and Melinda Gates Foundation.
Obama said it was essential to keep resisting efforts to scrap Obamacare.
"It may be frustrating that we have to mobilize every couple months to keep our leaders from inflicting real human suffering on their constituents," he said. "But typically, that's how progress is won."
Obama also warned Wednesday that nationalist sentiments could stymie efforts to combat poverty and disease.
"Nationalist thought, xenophobic sentiment ... a politics that threatens to turn good people away from the kind of collective action that has always driven human progress," Obama said.
Obama said it was essential to maintain an optimistic view in the face of hostile forces.
"We just have to reject the notion that we are suddenly gripped by forces that we can't control, and embrace the longer, more optimistic view of history and the part that we play in it," he said.
He insisted that America is a better place to live now than it ever has been, despite an onslaught of bad news.
"I know that statement doesn't seem to jibe with the steady stream of bad news and cynicism we're fed on television and Twitter," he said.
The former president also addressd climate change, calling it the "threat that may define the contours of this century more than any other."
Without a direct rebuke of President Donald Trump, Obama said that individuals and organizations must continue working on solutions to climate change, even if the US government has disengaged on the issue.
Speaking an event sponsored by the Bill and Melinda Gates Foundation, he quipped the Paris agreement was a "small agreement to save the planet."
"Even if the federal government is not as engaged on these efforts as I would like," the world is still making progress, Obama said.
Obama has reemerged in public infrequently since leaving the White House in January, focused instead on writing a memoir and traveling. He has spoken at a smattering of events for his own foundation, and appeared in Europe in May with German Chancellor Angela Merkel.
This fall, Obama is due to appear more, holding events for Democrats running in an off-election year, including gubernatorial candidates in New Jersey and Virginia.
When he's spoken in public, Obama has avoided criticizing his successor Donald Trump, though he has released statements on Facebook decrying decisions Trump has made over the course of his presidency.
He was sharply critical of Trump's plan to end a program shielding certain young immigrants from deportation, and he has been critical of attempts to repeal and replace the Affordable Care Act, the signature legislative accomplishment of his presidency.
In other areas, however, Obama has expressed more veiled displeasure. He didn't respond directly to Trump's equivocal comments about white supremacist violence in Virginia, instead tweeting a quote from Nelson Mandela (the tweet became the most liked of all time).
The two men have not spoken since the handoff of power on Inauguration Day, and their relationship is marked more by animosity than a shared respect at having both held the same office.
On Wednesday, Obama is expected to address the importance of supporting global development initiatives, including those highlighted by the Gates Foundation in their report.
The "Goalkeepers" report assesses a set of indicators pegged to the Global Goals, targets set by the United Nations in 2015 focused on reducing poverty and improving health. The report tracks statistics on child mortality, HIV rates and other areas to identify areas of need and single out successful methods for success.
Other speakers at Tuesday's event include Canadian Prime Minister Justin Trudeau, with whom Obama enjoyed a friendship while in office, and Malala Yousafzai, the Pakistani female education activist.
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