I was once in Washington D.C. on July 4th, I did not stay for the whole day. It was way too hot, way too busy (& dirty). While I was interning, I was staying with family in Virginia and my friend came to visit me. We took the train into D.C. for Independence Day. However, over 100 degrees, with no restaurants or stores opened, you are stuck with porta potties or the train stations bathrooms. This is not a desirable position to be in. We arrived by 1pm and left by 3pm. It was way too hot to do anything, not enough water or ice cream stands despite being in every other corner. We didn’t even bring blankets to sit on and forget about getting to sit on a bench at park.
We went home, watching the fireworks on television in an air conditioned couch. We were sad that we didn’t stay because it looked like it would have been a beautiful show but comfort beats anything in 100 degree weather. The next day, I heard from people who did stay for the show took over four hours to get home because the trains were so crowded and there was so much traffic. My advice is to book a hotel for D.C. and way ahead of time for the week of July 4th. There are plenty of free museums and the ones you need to pay are well worth your buck. My favorites are the International Spy Museum, The Museum of Crime and Punishment and the Newseum. Great capital, great public transportation, just not that great on July 4th but if you are staying in a hotel, well worth it!