The program, created under a 1997 law passed with bipartisan support during the administration of President Bill Clinton, provided coverage for children in families with low and moderate incomes as well as to pregnant women. It was instrumental in lowering the percentage of children who were uninsured from nearly 14 percent when it started to 4.5 percent in 2015. It was last reauthorized in 2015 and was due to be renewed by Sept. 30, 2017.

Most of the media coverage is saying that Congress "allowed the program to expire," but that's crap. The House chose not to renew funding, meaning they made a decision that at least temporarily killed the program. States can use any leftover money they currently have to fill the gap, but according to Medicaid officials quoted in the LA Times, California, Arizona, Minnesota, and North Carolina (plus DC according to the Post) will run out at the end of this year. A majority of states will run out by March 2018.

The LA Times continues:

What happened? The simple answer is that congressional Republicans’ last harebrained attempt to repeal the Affordable Care Act got in the way. A funding bill for CHIP seemed to be well on its way to enactment until a week or so ago. That’s when the effort to pass the egregious Cassidy-Graham repeal bill sucked all the air out of the legislative room.

Agreement on a bill had been reached in mid-September by Sens. Orrin Hatch (R-Utah) and Ron Wyden (D-Ore.). “Momentum was building,” says Bruce Lesley, president of First Focus, a children’s advocacy group in Washington. Then came Cassidy-Graham, and “we couldn’t even get a meeting,” Lesley says. “No one was even taking our calls.”

Meanwhile, that "compromise" measure still reduced funding, because the Republicans in Congress have fought against doing that, just as they've fought against making it permanent.

I'll let the times piece summarize:

Is there any more poignant example of how Congress’ wasteful partisanship affects ordinary Americans? It’s hard to imagine one. If the lawmakers can’t act in support of a program that was enacted in a spirit of bipartisanship and serves the most truly defenseless members of society, there’s no hope for them.