Barring congressional attempts to derail it, the fiercely debated and legally tested Patient Protection and Affordable Care Act is poised to take a major step toward full implementation on Jan. 1. Beginning Oct. 1, Americans can go online at government-regulated insurance “marketplaces,” or exchanges, and shop for insurance plans as an option to complying with the law’s “individual mandate,” a main focal point of the health care reform law and one that has passed U.S. Supreme Court review. Under the law, all Americans are required to have insurance or face IRS penalties that will escalate year to year.