Ideas for 4 hr layover in DC

Hey everyone. So I have a 4 hour layover in IAD coming back from Europe next month. I’ve never been to Washington DC before so I was just wondering if I could kill some time and see maybe something like a landmark or cool site while I’m there. I’ve always wanted to go just haven’t been able to. Would 4 hours be ok or is that cutting it close? I really don’t want to just be waiting at the airport that long before I go back to the west coast. Tips & info helpful for a 4 hour layover please! Places to see quickly but still enjoying my short time there!