Those currently covered are still funded. That's those in poverty, with some exceptions both up and down the scale (depending on state).
The only people "at risk" are those not currently funded. And it's not like they're under threat of anything except the risk of not getting additional Medicaid coverage. I have trouble saying that things that might exist already do exist. A bit too abstract when thinking about actual reality.
Then again, I think of threats as being of the form "Do this or I'll do this bad thing." Either you do something or I'll do something to hurt you or somebody else. That "bad thing" might be injuring the person your threatening or injuring somebody/something that the threatened person cares about.
The governor's threats were basically, "Rescind this provision or I'll be deprived of federal money and that will hurt the poor." It's oddly passive. It's not really a good threat.
Worded from the ACA's perspective you get, "Adopt this provision or I'll take away the federal money you already have and that will hurt the poor." That's a threat. It's the threat that Congress intended the bill to bear. It's not like Congress put that in there just so Obama could be the subject of a strangely worded not-quite-threat.
But I agree, the poor would be those held hostage. Not the poorest of the poor, for the most part, but that varies by state. There's a lot of this kind of mercenary hostage-taking in contemporary American politics, a hostage-taking that depends on its efficacy by virtue of framing and spin. "I make the threat, but I intend to show that the threat is reasonable and not complying with my threat is the real danger." Sometimes it works sometimes it doesn't. But this incessant treating of people as chattel really has to stop.