Worry that Obamacare is on life support doesn’t seem to scare Centene Corporation (NYSE: CNC) CEO Michael Neidorff. Over the past few years, he’s been significantly increasing Centene’s exposure to the exchanges, and at a time when other insurers are retreating from the Affordable Care Act, that’s translating into big money for the insurer. Here’s Centene’s secret to success and why investors might want to stash its shares in their portfolio.