One of the uncommitted superdelegates, Sen. Frank Lautenberg, was engaged in a primary fight for re-election Tuesday night and says he will make an endorsement soon.
Obama cinched the Democratic presidential nomination Tuesday, according to an Associated Press tally.
Holt says he stayed neutral while the nominating contest played out in primaries across the country, but says he feels superdelegates must weigh in to move the nominating process forward.
Holt called Clinton on Tuesday to tell her he is supporting her rival. The congressman says Clinton was "very gracious."
