The Associated Press

FILE - In this Oct. 8, 2010 file photo, Chief Justice John Roberts is seen during the group portrait at the Supreme Court Building in Washington. Breaking with the court's other conservative justices, Roberts announced the judgment that allows the law to go forward with its aim of covering more than 30 million uninsured Americans. Roberts explained at length the court's view of the mandate as a valid exercise of Congress' authority to "lay and collect taxes." The administration estimates that roughly 4 million people will pay the penalty rather than buy insurance. (AP Photo/Pablo Martinez Monsivais, File)

By NANCY BENAC Associated Press

WASHINGTON (AP) — As a junior senator, Barack Obama voted against John Roberts’ nomination to the Supreme Court, fearing he would favor the powerful over the weak.

Now it is Roberts who has saved the signature achievement of Obama’s presidency, the health care overhaul, in a ruling that challenges critics’ assertions that the chief justice is nothing more than a conservative ideologue.

Roberts had pledged at his 2005 confirmation hearing to act as a judicial umpire, calling balls and strikes without taking sides. On Thursday, he threw conservatives a curveball.

In a 5-4 ruling upholding the health care law, Roberts wrote for the majority that it’s not the court’s job to decide whether Obama’s plan ‘‘embodies sound policies. That judgment is entrusted to the nation’s elected leaders.’’