While speaking at an event sponsored by the Bill and Melinda Gates Foundation today, former President Barack Obama said "people are alive today because of" the Affordable Care Act, "and when I see people trying to undo that hard-won progress…it is aggravating."

Obama ripped into the Graham-Cassidy bill, which proposes block grant funding to be distributed among the states. Obama said it would "raise costs, reduce coverage and roll back protections for older Americans, and people with pre-existing conditions." Based on current projections from consulting firm Avalere Health, health care cuts could top $4 trillion under this bill.

Other key quotes:

"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."

... a politics that threatens to turn good people away from the kind of collective action that has always driven human progress." On climate change: It's the "threat that may define the contours of this century more than any other."

It's the "threat that may define the contours of this century more than any other." On the future of the internet: "I don't think we can count on conventional media to spread the word [of progress]. This is where the power of the internet has not been harnessed the way it needs to be, particularly when you think of young people and young audiences.

Watch Obama speak:

Obama is speaking across town from Trump's UN appearance.