During the rally Monday, the former president said Obamacare is causing premiums to rise because of the exchange markets.
"It doesn't make any sense. The insurance model doesn't work here," Clinton said.
"So you've got this crazy system where all of a sudden 25 million more people have healthcare and then the people who are out there busting it, sometimes 60 hours a week, wind up with their premiums doubled and their coverage cut in half. It's the craziest thing in the world," he said.
Clinton said on the other hand, "the current system works fine if you're eligible for Medicaid, if you're a lower-income working person; if you're already on Medicare, or if you get enough subsidies on a modest income that you can afford your health care. But the people that are getting killed in this deal are small business people and individuals who make just a little too much to get any of these subsidies."
He made the criticism while showing support for Hillary Clinton's "public option", which would allow individuals ages 55 to 65 to buy into Medicare directly. Also, others could purchase a government plan similar to Medicare.
Bill Clinton had worked with Hillary Clinton to overhaul healthcare in the 1990s but it wasn't approved because of opposition by Congress and the insurance lobby.
The Obama administration has publicly signaled willingness to change ACA but has been met with opposition.
"What I would also say is that since the very first day the president signed this bill into law, he acknowledged an openness to working with Democrats or Republicans in Congress to further strengthen it," White House press secretary Josh Earnest said at a briefing Monday before Bill Clinton's comments. "And we have seen a sustained commitment on the part of Republicans to trying to tear down that law."
The Republican National Committee noted Bill Clinton's comments and video of them on its website.
Republican nominee Donald Trump has called for the complete repeal of Obamacare. He proposes doing away with the government mandate requiring all individual to purchase insurance or face a fine, and plans to reduce the cost of insurance without intensive government regulations.