"He loved and honored his country even when the feeling was unreturned, and counseled others to do the same," said Senator McCain.
Senator Barack Obama is in Indiana. Evoking the memory of Robert F. Kennedy who announced Dr. King's death to a crowd gathered in the same state four decades ago.
On the same day it was announced that the U.S. had lost 80,000 jobs in March, the most in five years and the third straight month of losses.
Obama highlighted Dr. King's focus on economic equality by saying, "The struggle for economic justice remains an unfinished part of Dr. King's legacy. The dream is still out of reach for many Americans."
Obama's lead in votes, cash and momentum is bringing him support among super delegates. In the last two months, he's picked up 67 super delegates and Clinton, has lost seven.
More bad news for Clinton, another two of her pledged super delegates are hinting they may switch to Obama, if Clinton doesn't win the popular vote.