The final lines of the movie, said as the shot of Cap fades into his comic book form:
Radio Newscaster: In Rome today, one hundred and sixteen nations agreed to an environmental protection treaty. In a brief statement after the signing, President Kimball asked that we remember the many people who have gallantly sacrificed all to make our world a better place to live. The president closed his statement with this odd message: "To Captain America, wherever he may be... we're all back in the fight."
The fact that Kimball stays to back up Cap despite his urging to get out while the getting's good.