OKLAHOMA CITY (AP) — Despite bitter resistance in Oklahoma for years to President Barack Obama's health care overhaul, Republican leaders in this conservative state are now confronting something that alarms them even more: a huge $1.3 billion hole in the budget that threatens to do widespread damage to the state's health care system. [...] in what would be the grandest about-face among rightward leaning states, Oklahoma is now moving toward a plan to expand its Medicaid program to bring in billions of federal dollars from Obama's new health care system. Obama called on states to expand their Medicaid insurance for low-income residents as part of his 2014 health overhaul designed to shrink the population of uninsured Americans. [...] in Oklahoma, even with 20 percent of its population on Medicaid, it's been no way, no how. [...] . Americans for Prosperity, another conservative think-tank backed by the billionaire philanthropist Koch brothers, David and Charles, also has launched a campaign against the proposal and is hosting a "NobamaCare" event at the state Capitol to voice their opposition.