I'd never want that connecting time before an international flight; they generally want everyone onboard by the 45-minute mark. It looks like the DCA-EWR flights are all Express flights, which mostly go to Terminal A, and your departure would be from C. There is a bus that keeps you from needing to re-clear security, but I'd say that isn't a reasonable connection time.
The one recent time that I had a connecting time, as a result of a schedule change, that was legal but not reasonable, I was able to get it changed without penalty.