Word of the endorsement came on the same day that Clinton called for delegates from Florida and Michigan to be seated at the Democratic National Convention. The national party punished Florida Democrats for scheduling their primary before Feb. 5 by stripping all 210 delegates to the convention.
Nelson and Rep. Alcee Hastings, D-Fla., had filed a lawsuit in federal court against the Democratic National Committee, but a federal judge ruled in favor of the DNC for stripping the state of delegates for the convention.
All the major Democratic candidates made pledges not to campaign in those states before their primaries.
Clinton could claim most of the Michigan delegates because she won that state's primary after the other major candidates pulled their names from the ballot.
"I know other campaigns have tried to downplay the significance of these two states," Clinton told reporters in South Carolina Friday. "I think that is not a good strategy for Democrats or any of us who cares about the outcome of this election."
Nelson was elected to the Senate in 2000, the same year Clinton won her New York seat, and the two serve on the Senate Armed Services Committ. A moderate Democrat, he was a crew member of the Space Shuttle Columbia in 1986.
