Rep. John Lewis had gone largely silent on Michael Boggs nomination.
One of Obama's judicial picks has hit a wall over past positions.
Statements from several Democrats suggest the nomination could be in trouble.
Michael Boggs is one of seven judicial nominees scheduled to appear before the Senate panel.
Obama nominated Boggs to Georgia's federal bench in December.
Top black Dems this week reentered the public fight against an embattled Georgia judge.
The Senate leader said he "can't vote" for Michael Boggs at this point in time.
CBC members upset over controversial judge Michael Boggs's nomination.
A Democratic lawmaker is accusing the Obama administration of being "dishonest" in the handling of...