Detroit, July 25 -- Joe Biden rarely lets a public event pass without reminding voters of his work alongside President Barack Obama. But the former vice president insisted on Wednesday that he's not overly relying on that relationship to fuel his 2020 White House bid.

"It's not a crutch," Biden said during a forum in Detroit sponsored by the NAACP. "You can ask President Obama. I don't need any crutch."

The comment reflects the challenge facing Biden as he tries to protect his fragile status as the early Democratic front-runner. His frequent invocation of the Obama years could appeal to Democrats, particularly African Americans, who hold the former president in high regard. But presidential candidates aren't often successful if they're ...