Thom Hartmann:
When the ACA was rolled out, telling insurance companies that they had to insure anybody who signed up, regardless of previous conditions or sickness, everybody realized that the insurance companies would probably lose money in the first decade or so, until previously-uninsured-but-sick people got into the system, got better, and things evened out.
To get the insurance companies to go along with this danger of losing money, the ACA promised to make them whole for any losses in any of the first decade's years. At the end of each fiscal year, the insurance companies merely had to document their losses, and the government would reimburse them out of ACA funds provided for by the law.
The possibility of their losing money was referred to as the "risk corridor," and the ACA explicitly filled those risk corridors with a guarantee of making the insurance companies, at the very least, whole.
And then something happened. As The New York Times noted on December 9, 2015, "A little-noticed health care provision slipped into a giant spending law last year has tangled up the Obama administration, sent tremors through health insurance markets and rattled confidence in the durability of President Obama’s signature health law."
Rubio and a number of other Republicans had succeeded in gutting the risk corridors. The result was that, just in 2015, end-of-fiscal-year risk corridor payments to insurance companies that were supposed to total around $2.9 billion were only reimbursed, according to Rubio himself quoted in the Times, to the tune of around $400 million. Rubio bragged that he'd "saved taxpayers $2.5 billion."
And, indeed, he had. But the insurance companies were thrown into a crisis. And, with Republicans in Congress absolutely refusing to re-fund the risk corridors, that crisis would get worse as time went on, at least over a period of a few years.
So the insurance companies did the only things they could. In (mostly red) states with low incomes and thus poorer health, they simply pulled out of the marketplace altogether. This has left some states with only one single insurer left. In others, they jacked up their prices to make up their losses.
As Robert Pear in the Times noted, Rubio's "plan limiting how much the government can spend to protect insurance companies against financial losses has shown the effectiveness of quiet legislative sabotage."
To add to the political psychodrama, the first hack by Rubio was maintained by Republicans into the 2016 budget, meaning that things got even worse in October, 2016 – the first month of the federal fiscal year when these cuts hit the worse, and, no coincidence, the month before the presidential election.
Rubio's October Surprise was extraordinarily effective. October 2016 saw an explosion of stories in the news about how health insurance companies were either pulling out of ACA exchanges, or jacking their prices up wildly.