WASHINGTON — President Barack Obama praised outgoing Health and Human Secretary Kathleen Sebelius for helping to steer his health care law’s comeback after a rocky rollout, even as he nominated a successor aimed at helping the White House move past the political damage.“Under Kathleen’s leadership, her team at HHS turned the corner, got it fixed, got the job done,” Obama said in a Rose Garden ceremony Friday morning. “And the final score speaks for itself.”About 7.5 million people have signed up for health insurance through the new law, exceeding expectations after website woes stymied sign-ups for week when enrollment opened last fall. Obama nominated his budget chief, Sylvia Mathews Burwell, to replace Sebelius, calling her “a proven manager” who knows how to get results. The nomination of Burwell, who was unanimously confirmed by the Senate for her current post last year, appeared aimed at avoiding an election-year confirmation fight.“Last time, she was confirmed unanimously,” Obama said. “I’m assuming not much has changed since that time.”Sebelius, who has served as Obama’s health and human services chief for five years, was instrumental in steering the sweeping health law through Congress in 2010. But her tenure was marred by widespread technical problems that crippled the sign-up website for weeks, sparking calls from Republicans for Sebelius’ resignation.