From WTOP News
"The park service’s Mike Litterst warns that there will be no crossing the parade route at all. So if you plan to attend the rally, expect to do so from the south side.
The fencing will be up from 23rd to Sixth streets. It will be impenetrable, and will not allow any crossing of the parade route. Cross streets will close at 9:30 a.m. Tuesday, according to the park service.
There will be no alcohol, no glass and no drones allowed."
So if you want to watch the parade and then go to the rally, you need to get on the south side of Constitution Avenue or the Washington Monument/Mall side of Constitution avenue. If you watch from the north side it appears you won't be allowed to cross Constitution Avenue, however I have to think that once the parade arrives at the rally site on the Mall, they're not going to continue to keep Constitution Avenue closed to pedestrians crossing.