Under Article 2, Obama has the power to do so.
From report at LINK in Post #1:
“......Tom and Joe Connor, two brothers who were little boys when their 33-year-old father, Frank, was killed in the Fraunces Tavern attack, were dumbstruck to learn that White House staffers referred to the FALN militants as “political prisoners” and were planning a meeting with their children to humanize their plight.
Members of Congress viewed the clemencies as a dangerous abuse of presidential power that could not go unchallenged. Resolutions condemning the president’s action were passed with a vote of 95-2 in the Senate, 311-41 in the House. It was the most they could do; the president’s pardon power, conferred by the Constitution, is absolute. The House launched an investigation, subpoenaing records from the White House and Justice in an effort to determine whether proper procedure had been followed. President Clinton promptly invoked executive privilege, putting Justice Department lawyers in the impossible position of admitting that they had sent the White House a recommendation on the issue, but barred from disclosing what it was.
Twenty-four hours before a scheduled Senate committee hearing, the DOJ withheld the FBI’s written statement about the history of the FALN and an assessment of its current terrorist capability. “They pulled the plug on us,” said an unnamed FBI official in a news report, referring to the Justice Department decision to prevent FBI testimony.....”