"Frankly, he has not been around long enough to determine what my dignity is"

“Frankly, he has not been around long enough to determine what my dignity is,” Mr. Rangel said of the 49-year-old Mr. Obama. “For the next two years, I will be more likely to protect his dignity.”

The unexpected eruption seemed to reflect the increasingly bitter relations between the embattled 20-term Democrat from Harlem and a president who is trying to protect his party’s prospects in a difficult midterm election season.

And it came during an uncomfortable evening for Mr. Rangel, who made a rare appearance with his five challengers and found himself facing harsh public attacks in front of his constituents at a Baptist church in the heart of his Harlem district.