WASHINGTON — President Barack Obama’s sweeping immigration executive orders, now slightly more than a week old, cap a turbulent, six-year quest to make headway on a thorny issue that has at times put the White House at odds with some of its fiercest supporters. To those who argue the actions are long overdue or don’t go far enough, Obama pins the blame solely on Republicans who oppose broader legislation. But Obama himself has contributed to the delays, making political calculations that left …