A Democratic senator has called on President Obama to “immediately condemn” the Internal Revenue Service for targeting conservative groups.

“The actions of the IRS are unacceptable and un-American. Government agencies using their bureaucratic muscle to target Americans for their political beliefs cannot be tolerated,” Sen. Joe Manchin (D-W.Va.) said today. “The president must immediately condemn this attack on our values, find those individuals in his administration who are responsible and fire them.”

The commissioner who was in charge during last campaign season, Douglas Shulman, left the administration three days after Obama was re-elected.

Manchin said the time is now to begin probing the scandal.

“While we await answers from the Inspector General, there must be a congressional investigation to determine how this happened and to prevent this from ever happening again,” he said.

Sen. Carl Levin (D-Mich.), chairman of the Senate Permanent Subcommittee on Investigations, issued on Friday a more careful statement calling for a probe into the IRS’ enforcement of nonprofit rules.

“My subcommittee has been investigating the IRS’s failure to enforce the law requiring that tax-exempt 501(c)4s be engaged exclusively in social welfare activities, not partisan politics,” Levin said. “Today’s announcement by the IRS raises a second issue: whether the IRS, to the extent it has enforced its rules, has been impartial in doing so. Both issues require investigation.”